JME¶
JME expressions are used by students to enter answers to algebraic questions, and by question authors to define variables. JME syntax is similar to what you’d type on a calculator.
Variable names¶
Variable names are caseinsensitive, so y
represents the same thing as Y
.
The first character of a variable name must be an alphabet letter; after that, any combination of letters, numbers and underscores is allowed, with any number of '
on the end.
 Examples:
x
x_1
time_between_trials
var1
row1val2
y''
e
, i
and pi
are reserved names representing mathematical constants.
They are rewritten by the interpreter to their respective numerical values before evaluation.
This screencast describes which variable names are valid, and gives some advice on how you should pick names:
Variable name annotations¶
Names can be given annotations to change how they are displayed. The following annotations are builtin:
verb
– does nothing, but names likei
,pi
ande
are not interpreted as the famous mathematical constants.op
– denote the name as the name of an operator — wraps the name in the LaTeX operatorname command when displayedv
orvector
– denote the name as representing a vector — the name is displayed in boldfaceunit
– denote the name as representing a unit vector — places a hat above the name when displayeddot
– places a dot above the name when displayed, for example when representing a derivativem
ormatrix
– denote the name as representing a matrix — displayed using a nonitalic font
Any other annotation is taken to be a LaTeX command.
For example, a name vec:x
is rendered in LaTeX as \vec{x}
, which places an arrow above the name.
You can apply multiple annotations to a single variable.
For example, v:dot:x
produces a bold x with a dot on top: \(\boldsymbol{\dot{x}}\).
Names with different annotations are considered to represent different values, for the purpose of simplification and evaluation.
For example, in the expression dot:x + x
, the two terms will not be collected together.
Data types¶
JME expressions are composed of the following data types. Some extensions add new data types.

number
¶ A real or complex floatingpoint number.
i
,e
,infinity
andpi
are reserved keywords for the imaginary unit, the base of the natural logarithm, ∞ and π, respectively.Examples:
0.0
,1.0
,0.234
,i
,e
,pi
Numbers of this type are represented using JavaScript’s builtin
Number
object, which is a 64bit IEEE 754 floatingpoint number. This representation offers a very good compromise between precision and the range of values that can be stored, but can behave in unexpected ways. Accuracy is easily lost when dealing with very big or very small numbers, and on division.See functions related to Arithmetic, Number operations, Trigonometry and Number theory.
 Automatically converts to:

integer
¶ An element of the set of integers, \(\mathbb{Z}\).
Examples:
0
,1
,2
, 431`.

rational
¶ A fraction; an element of the set of rationals, \(\mathbb{Q}\). The numerator and denominator are integers.
Instances of this data type may be topheavy, with numerator bigger than the denominator, and are not required to be reduced.
Examples:
1/1
,34/2
, 3/4`.

decimal
¶ A number with a guaranteed level of precision, and arbitrary order of magnitude.
Numbers of this type are represented using the Decimal.js library. They’re guaranteed to be accurate to 40 significant figures. The order of magnitude is stored separately from the significant digits, so there’s no less of precision for very big or very small numbers.
Examples:
dec(0)
,dec("1.23e5")
,6.0221409*10^23
 Automatically converts to:

boolean
¶ Booleans represent either truth or falsity. The logical operations and, or and xor operate on and return booleans.
Examples:
true
,false
See functions related to Logic and Control flow.

string
¶ Use strings to create nonmathematical text. Either
'
or"
can be used to delimit strings.You can escape a character by placing a single backslash character before it. The following escape codes have special behaviour:
\n
Newline \{
\{
\}
\}
If you want to write a string which contains a mixture of single and double quotes, you can delimit it with tripledoublequotes or triplesinglequotes, to save escaping too many characters.
Examples:
"hello there"
,'hello there'
,""" I said, "I'm Mike's friend" """
See functions related to Strings.

list
¶ An ordered list of elements of any data type.
Examples:
[0,1,2,3]
,[a,b,c]
,[true,false,true]
See functions related to Lists.

dict
¶ A ‘dictionary’, mapping key strings to values of any data type.
A dictionary is created by enclosing one or more keyvalue pairs (a string followed by a colon and any JME expression) in square brackets, or with the
dict
function.Key strings are casesensitive.
Examples:
["a": 1, "b": 2]
["name": "Tess Tuser", "age": 106, "hobbies": ["reading","writing","arithmetic"] ]
dict("key1": 0.1, "key2": 1..3)
dict([["key1",1], ["key2",2]])
Warning
Because lists and dicts use similar syntax,
[]
produces an empty list, not an empty dictionary. To create an empty dictionary, usedict()
.See functions related to Dictionaries and JSON.

range
¶ A range
a..b#c
represents (roughly) the set of numbers \(\{a+nc \:  \: 0 \leq n \leq \frac{ba}{c} \}\). If the step size is zero, then the range is the continuous interval \([a,b]\).Examples:
1..3
,1..3#0.1
,1..3#0
See functions related to Ranges.

set
¶ An unordered set of elements of any data type. The elements are pairwise distinct  if you create a set from a list with duplicate elements, the resulting set will not contain the duplicates.
Examples:
set(a,b,c)
,set([1,2,3,4])
,set(1..5)
See functions related to Sets.
 Automatically converts to:

vector
¶ The components of a vector must be numbers.
When combining vectors of different dimensions, the smaller vector is padded with zeros to make up the difference.
Examples:
vector(1,2)
,vector([1,2,3,4])
See functions related to Vector and matrix arithmetic.

matrix
¶ Matrices are constructed from lists of numbers, representing the rows.
When combining matrices of different dimensions, the smaller matrix is padded with zeros to make up the difference.
Examples:
matrix([1,2,3],[4,5,6])
,matrix(row1,row2,row3)
See functions related to Vector and matrix arithmetic.

name
¶ A variable name. When an expression is evaluated, all variable names are replaced withe their corresponding value in the current scope.

function
¶ An application of a function.
Examples:
f(x)
,sin(x)

op
¶ An infix binary operation, or a pre/postfix unary operation.
Examples:
x+y
,n!
,a and b

expression
¶ A JME subexpression. Subexpressions can be simplified, rearranged, patternmatched, or evaluated using given values for their free variables.
See functions related to Subexpressions.
Automatic data type conversion¶
Some data types can be automatically converted to others when required.
For example, the numberlike types such as integer
and decimal
can be automatically converted to number
values.
The data types of the arguments to a function application determine which version of the function is used. Ideally, this will do what you expect without you having to think about it. For reference, the process for deciding on what conversions to perform is as follows:
 If there is a version of the function which takes exactly the given data types, that is used.
 Otherwise, each definition of the function is compared by looking at each of the arguments, working from left to right.
 A definition which does not convert an argument is preferred to one that does.
 If both definitions being compared need to convert an argument, the type that occurs first in the input type’s list of automatic conversion methods is used. (This follows the order of the types under the “Automatically converts to” headers above)
The following examples illustrate how this works.
Expression  Type of result  Explanation 
1+3.3 
number 
The 1 is converted to a number , and then added to 3.3 . 
1+1/2 
rational 
integer prefers to convert to rational over 
1.23+dec("1.2") 
decimal 
decimal values are preferred to number because they’re more precise. 
1/2+0.5 
number 
rational can convert to number , but not the other way round, so number addition is used. 
set(1,2,3,4) except [2] 
list 
except() is only defined on list values, so the set is converted to a list automatically. 
Function reference¶
Arithmetic¶

x+y
Addition.
 Definitions:
number
,number
→number
list
,list
→list
 concatenate two listslist
, anything →list
 add an item to the end of a listdict
,dict
→dict
 merge two dictionaries, with values from the righthand side taking precedence when the same key is present in both dictionaries.string
, anything →string
 convert the righthand argument to a string, and concatenate anything,
string
→string
 convert the lefthand argument to a string, and concatenate vector
,vector
→vector
matrix
,matrix
→matrix
integer
,integer
→integer
rational
,rational
→rational
decimal
,decimal
→decimal
number
,decimal
→decimal
 Examples:
1+2
→3
vector(1,2)+vector(3,4)
→vector(4,6)
matrix([1,2],[3,4])+matrix([5,6],[7,8])
→matrix([6,8],[10,12])
[1,2,3]+4
→[1,2,3,4]
[1,2,3]+[4,5,6]
→[1,2,3,4,5,6]
"hi "+"there"
→"hi there"

xy
Subtraction.
 Definitions:
 Examples:
12
→1
vector(3,2)vector(1,4)
→vector(2,2)
matrix([5,6],[3,4])matrix([1,2],[7,8])
→matrix([4,4],[4,4])

x*y
Multiplication.
 Definitions:
number
,number
→number
number
,vector
→vector
vector
,number
→vector
matrix
,vector
→vector
number
,matrix
→matrix
matrix
,number
→matrix
matrix
,matrix
→matrix
vector
,matrix
→vector
integer
,integer
→integer
rational
,rational
→rational
decimal
,decimal
→decimal
number
,decimal
→decimal
 Examples:
1*2
→2
2*vector(1,2,3)
→vector(2,4,6)
matrix([1,2],[3,4])*2
→matrix([2,4],[6,8])
matrix([1,2],[3,4])*vector(1,2)
→vector(5,11)

x/y
Division. Only defined for numbers.
Number operations¶

decimal
(n) 
decimal
(x) Construct a
decimal
value. Any string accepted by Decimal.js is accepted.

int
(n)¶ Convert
n
to an integer, rounding to the nearest integer.

abs
(x)¶ 
len
(x)¶ 
length
(x)¶ Absolute value, or modulus.
 Definitions:
 Examples:
abs(8)
→8
abs(34i)
→5
abs("Hello")
→5
abs([1,2,3])
→3
len([1,2,3])
→3
len(set([1,2,2]))
→2
length(vector(3,4))
→5
abs(vector(3,4,12))
→13
len(["a": 1, "b": 2, "c": 1])
→3

isint
(x)¶ Returns
true
ifx
is an integer  that is, it is real and has no fractional part.

log
(x, b)¶ Logarithm with base
b
, or base 10 ifb
is not given.

log
(x, b) Logarithm with base
b
. Example:
log(8,2)
→3
.

radians
(x)¶ Convert degrees to radians.
 Example:
radians(180)
→pi

max
(a, b)¶ Greatest of the given numbers.

min
(a, b)¶ Least of the given numbers.

clamp
(x, a, b)¶ Return the point nearest to
x
in the interval \([a,b]\).Equivalent to
max(a,min(x,b))
.

precround
(n, d)¶ Round
n
tod
decimal places. On matrices and vectors, this rounds each element independently.

siground
(n, f)¶ Round
n
tof
significant figures. On matrices and vectors, this rounds each element independently.

withintolerance
(a, b, t)¶ Returns
true
if \(bt \leq a \leq b+t\).

dpformat
(n, d[, style])¶ Round
n
tod
decimal places and return a string, padding with zeros if necessary.If
style
is given, the number is rendered using the given notation style. See the page on Number notation for more on notation styles.

countdp
(n)¶ Assuming
n
is a string representing a number, return the number of decimal places used. The string is passed throughcleannumber()
first.

sigformat
(n, d[, style])¶ Round
n
tod
significant figures and return a string, padding with zeros if necessary.

countsigfigs
(n)¶ Assuming
n
is a string representing a number, return the number of significant figures. The string is passed throughcleannumber()
first.

togivenprecision
(str, precisionType, precision, strict)¶ Returns
true
ifstr
is a string representing a number given to the desired number of decimal places or significant figures.precisionType
is either"dp"
, for decimal places, or"sigfig"
, for significant figures.If
strict
istrue
, then trailing zeroes must be included.

tonearest
(a, b)¶ Round
a
to the nearest multiple ofb
.

formatnumber
(n, style)¶ Render the number
n
using the given number notation style.See the page on Number notation for more on notation styles.

cleannumber
(str, styles)¶ Clean a string potentially representing a number. Remove space, and then try to identify a notation style, and rewrite to the
plainen
style.styles
is a list of notation styles. Ifstyles
is given, str will be tested against the given styles. If it matches, the string will be rewritten using the matched integer and decimal parts, with punctuation removed and the decimal point changed to a dot.

matchnumber
(str, styles)¶ Try to match a string representing a number in any of the given styles at the start of the given string, and return both the matched text and a corresponding
number
value.

parsenumber
(string, style)¶ Parse a string representing a number written in the given style.
If a list of styles is given, the first that accepts the given string is used.
See the page on Number notation for more on notation styles.
 Examples:
parsenumber("1 234,567","sifr")
→1234.567
parsenumber("1.001",["sifr","eu"])
→1001

parsenumber_or_fraction
(string, style)¶ Works the same as
parsenumber()
, but also accepts strings of the formnumber/number
, which it interprets as fractions. Example:
parsenumber_or_fraction("1/2")
→0.5

parsedecimal
(string, style)¶ Parse a string representing a number written in the given style, and return a
decimal
value.If a list of styles is given, the first that accepts the given string is used.
See the page on Number notation for more on notation styles.

parsedecimal_or_fraction
(string, style)¶ Works the same as
parsedecimal()
, but also accepts strings of the formnumber/number
, which it interprets as fractions.
Trigonometry¶
Trigonometric functions all work in radians, and have as their domain the complex numbers.

tan
(x)¶ Tangent: \(\tan(x) = \frac{\sin(x)}{\cos(x)}\)

arcsin
(x)¶ Inverse of
sin()
. When \(x \in [1,1]\),arcsin(x)
returns a value in \([\frac{\pi}{2}, \frac{\pi}{2}]\).

arccos
(x)¶ Inverse of
cos()
. When \(x \in [1,1]\),arccos(x)
returns a value in \([0, \frac{\pi}]\).

arctan
(x)¶ Inverse of
tan()
. When \(x\) is noncomplex,arctan(x)
returns a value in \([\frac{\pi}{2}, \frac{\pi}{2}]\).

sinh
(x)¶ Hyperbolic sine: \(\sinh(x) = \frac{1}{2} \left( \mathrm{e}^x  \mathrm{e}^{x} \right)\)

cosh
(x)¶ Hyperbolic cosine: \(\cosh(x) = \frac{1}{2} \left( \mathrm{e}^x + \mathrm{e}^{x} \right)\)

tanh
(x)¶ Hyperbolic tangent: \(\tanh(x) = \frac{\sinh(x)}{\cosh(x)}\)

cosech
(x)¶ Hyperbolic cosecant: \(\operatorname{cosech}(x) = \frac{1}{\sinh(x)}\)

sech
(x)¶ Hyperbolic secant: \(\operatorname{sech}(x) = \frac{1}{\cosh(x)}\)
Number theory¶

x!
Factorial. When
x
is not an integer, \(\Gamma(x+1)\) is used instead.fact(x)
is a synoynm forx!
.

factorise
(n)¶ Factorise
n
. Returns the exponents of the prime factorisation ofn
as a list.

gamma
(x)¶ Gamma function.

ceil
(x)¶ Round up to the nearest integer. When
x
is complex, each component is rounded separately.

floor
(x)¶ Round down to the nearest integer. When
x
is complex, each component is rounded separately.

round
(x)¶ Round to the nearest integer.
0.5
is rounded up.

trunc
(x)¶ If
x
is positive, round down to the nearest integer; if it is negative, round up to the nearest integer.

fract
(x)¶ Fractional part of a number. Equivalent to
xtrunc(x)
.

rational_approximation
(n[, accuracy])¶ Compute a rational approximation to the given number by computing terms of its continued fraction, returning the numerator and denominator separately. The approximation will be within \(e^{\text{accuracy}}\) of the true value; the default value for
accuracy
is 15.

mod
(a, b)¶ Modulo; remainder after integral division, i.e. \(a \bmod b\).

perm
(n, k)¶ Count permutations, i.e. \(^n \kern2pt P_k = \frac{n!}{(nk)!}\).

comb
(n, k)¶ Count combinations, i.e. \(^n \kern2pt C_k = \frac{n!}{k!(nk)!}\).

gcd_without_pi_or_i
(a, b)¶ Take out factors of \(\pi\) or \(i\) from
a
andb
before computing their greatest common denominator.

coprime
(a, b)¶ Are
a
andb
coprime? True if theirgcd()
is \(1\), or if either ofa
orb
is not an integer.

lcm
(a, b)¶ Lowest common multiple of integers
a
andb
. Can be used with any number of arguments; it returns the lowest common multiple of all the arguments.
Vector and matrix arithmetic¶

vector
(a1, a2, ..., aN) Create a vector with given components. Alternately, you can create a vector from a single list of numbers.

matrix
(row1, row2, ..., rowN) Create a matrix with given rows, which should be either vectors or lists of numbers. Or, you can pass in a single list of lists of numbers.

id
(n)¶ Identity matrix with \(n\) rows and columns.

numrows
(matrix)¶ The number of rows in the given matrix

numcolumns
(matrix)¶ The number of columns in the given matrix

rowvector
(a1, a2, ..., aN)¶ Create a row vector (\(1 \times n\) matrix) with the given components. Alternately, you can create a row vector from a single list of numbers.

dot
(x, y)¶ Dot (scalar) product. Inputs can be vectors or column matrices.

cross
(x, y)¶ Cross product. Inputs can be vectors or column matrices.

angle
(a, b)¶ Angle between vectors
a
andb
, in radians. Returns0
if eithera
orb
has length 0.

is_zero
(x)¶ Returns
true
if every component of the vectorx
is zero.

det
(x)¶ Determinant of a matrix. Throws an error if used on anything larger than a 3×3 matrix.

transpose
(x)¶ Matrix transpose.
Strings¶

x[n]
Get the Nth character of the string
x
. Indices start at 0. Example:
"hello"[1]
→"e"

x[a..b]
Slice the string
x
 get the substring between the given indices. Note that indices start at 0, and the final index is not included. Example:
"hello"[1..4]
→"ell"

substring in string
Test if
substring
occurs anywhere instring
. This is casesensitive. Example:
"plain" in "explains"
→true

string
(x) Convert
x
to a string.

latex
(x)¶ Mark string
x
as containing raw LaTeX, so when it’s included in a mathmode environment it doesn’t get wrapped in a\textrm
environment.Note that backslashes must be double up, because the backslash is an escape character in JME strings.

safe
(x)¶ Mark string
x
as safe: don’t substitute variable values into it when this expression is evaluated.Use this function to preserve curly braces in string literals.

render
(x, values)¶ Substitute variable values into the string
x
, even if it’s marked as safe (seesafe()
).The optional dictionary
values
overrides any previouslydefined values of variables. Definitions:
 Example:
render(safe("I have {num_apples} apples."), ["num_apples": 5])
→"I have 5 apples."
render(safe("Let $x = \\var{x}$"), ["x": 2])
→"Let $x = {2}$"
Note
The variable dependency checker can’t establish which variables will be used in the string until
render
is evaluated, so you may encounter errors if usingrender
in the definition of a question variable. You can ensure a variable has been evaluated by including it in thevalues
argument, e.g.:render("a is {}",["a": a])
This function is intended for use primarily in content areas.

capitalise
(x)¶ Capitalise the first letter of a string.

pluralise
(n, singular, plural)¶ Return
singular
ifn
is 1, otherwise returnplural
.

lower
(x)¶ Convert string to lowercase.

join
(strings, delimiter)¶ Join a list of strings with the given delimiter.

split
(string, delimiter)¶ Split a string at every occurrence of
delimiter
, returning a list of the the remaining pieces.

trim
(str)¶ Remove whitespace from the start and end of
str
.

currency
(n, prefix, suffix)¶ Write a currency amount, with the given prefix or suffix characters.

separateThousands
(n, separator)¶ Write a number, with the given separator character between every 3 digits
To write a number using notation appropriate to a particular culture or context, see
formatnumber()
.

unpercent
(str)¶ Get rid of the
%
on the end of a percentage and parse as a number, then divide by 100.

lpad
(str, n, prefix)¶ Add copies of
prefix
to the start ofstr
until the result is at leastn
characters long.

rpad
(str, n, suffix)¶ Add copies of
suffix
to the end ofstr
until the result is at leastn
characters long.

formatstring
(str, values)¶ For each occurrence of
%s
instr
, replace it with the corresponding entry in the listvalues
.

letterordinal
(n)¶ Get the \(n\)^{th} element of the sequence
a, b, c, ..., aa, ab, ...
.Note that the numbering starts from 0.

match_regex
(pattern, str, flags)¶ If
str
matches the regular expressionpattern
, returns a list of matched groups, otherwise returns an empty list.This function uses JavaScript regular expression syntax.
flags
is an optional string listing the options flags to use.

translate
(str, arguments)¶ Translate the given string, if it’s in the localisation file.
Look at the default localisation file for strings which can be translated. This function takes a key representing a string to be translated, and returns the corresponding value from the current localisation file.
arguments
is a dictionary of named substitutions to make in the string.
Logic¶

x<y
Returns
true
ifx
is less thany
.

x>y
Returns
true
ifx
is greater thany
.

x<=y
Returns
true
ifx
is less than or equal toy
.

x>=y
Returns
true
ifx
is greater than or equal toy
.

x<>y
Returns
true
ifx
is not equal toy
. Returnstrue
ifx
andy
are not of the same data type. Definitions:
 anything, anything →
boolean
 anything, anything →
 Examples:
'this string' <> 'that string'
1<>2
'1' <> 1

x=y
Returns
true
ifx
is equal toy
. Returnsfalse
ifx
andy
are not of the same data type. Definitions:
 anything, anything →
boolean
 anything, anything →
 Examples:
vector(1,2)=vector(1,2,0)
4.0=4

isclose
(x, y, rel_tol, abs_tol)¶ Returns
true
ifx
is close toy
.Equivalent to the following expression:
abs(xy) <= max( rel_tol*max(abs(a),abs(b)), abs_tol )

resultsequal
(a, b, checkingFunction, accuracy)¶ Returns
true
ifa
andb
are both of the same data type, and “close enough” according to the given checking function.Vectors, matrices, and lists are considered equal only if every pair of corresponding elements in
a
andb
is “close enough”.checkingFunction
is the name of a checking function to use. These are documented in the Numbas runtime documentation.

x and y

x && y

x & y
Logical AND. Returns
true
if bothx
andy
are true, otherwise returnsfalse
.

x or y
Logical OR. Returns
true
when at least one ofx
andy
is true. Returns false when bothx
andy
are false.

x xor y
Logical XOR. Returns
true
when at eitherx
ory
is true but not both. Returnsfalse
whenx
andy
are the same expression.
Collections¶

x[y]
Get the
y
^{th} element of the collectionx
.For matrices, the
y
^{th} row is returned.For dictionaries, the value corresponding to the key
y
is returned. If the key is not present in the dictionary, an error will be thrown.

x[a..b]

x[a..b#c]
Slice the collection
x
 return elements with indices in the given range. Note that list indices start at 0, and the final index is not included.

x in collection
Is element
x
incollection
? Definitions:
 Examples:
3 in [1,2,3,4]
→true
3 in (set(1,2,3,4) and set(2,4,6,8))
→false
"a" in ["a": 1]
→true
1 in ["a": 1]
throws an error because dictionary keys must be strings.
Ranges¶

a..b
Define a range. Includes all integers between and including
a
andb
.

range#step
Set the step size for a range. Default is 1. When
step
is 0, the range includes all real numbers between the limits.

a except b
Exclude a number, range, or list of items from a list or range.
 Definitions:
 Examples:
9..9 except 0
9..9 except [1,1]
3..8 except 4..6
[1,2,3,4,5] except [2,3]
Lists¶

repeat
(expression, n)¶ Evaluate
expression
n
times, and return the results in a list.

all
(list)¶ Returns
true
if every element oflist
istrue
.

some
(list)¶ Returns
true
if at least one element oflist
istrue
.

map
(expression,name[s],d)¶ Evaluate
expression
for each item in list, range, vector or matrixd
, replacing variablename
with the element fromd
each time.You can also give a list of names if each element of
d
is a list of values. The Nth element of the list will be mapped to the Nth name.Note
Do not use
i
ore
as the variable name to map over  they’re already defined as mathematical constants!

filter
(expression, name, d)¶ Filter each item in list or range
d
, replacing variablename
with the element fromd
each time, returning only the elements for whichexpression
evaluates totrue
.Note
Do not use
i
ore
as the variable name to map over  they’re already defined as mathematical constants!

take
(n, expression, name, d)¶ Take the first
n
elements from list or ranged
, replacing variablename
with the element fromd
each time, returning only the elements for whichexpression
evaluates totrue
.This operation is lazy  once
n
elements satisfying the expression have been found, execution stops. You can use this to filter a few elements from a large list, where the condition might take a long time to calculate.Note
Do not use
i
ore
as the variable name to map over  they’re already defined as mathematical constants!

let
(name, definition, ..., expression)¶ 
let
(definitions, expression) Evaluate
expression
, temporarily defining variables with the given names. Use this to cut down on repetition. You can define any number of variables  in the first calling pattern, follow a variable name with its definition. Or you can give a dictionary mapping variable names to their values. The last argument is the expression to be evaluated.

sort_destinations
(x)¶ Return a list giving the index that each entry in the list will occupy after sorting.

sort_by
(key, list)¶ Sort the given list of either
list
ordict
values by their entries corresponding to the given key. When sorting a list of lists, the key is a number representing the index of each list to look at. When sorting a list of dictionaries, the key is a string. Definitions:
 Examples:
sort_by(0, [[5,0], [3,2], [4,4]])
→[[3,2], [4,4], [5,0]]
sort_by("width", [["label": "M", "width": 20], ["label": "L", "width": 30], ["label": "S", "width": 10]])
→[["label": "S", "width": 10], ["label": "M", "width": 20], ["label": "L", "width": 30]]

group_by
(key, list)¶ Group the entries in the given list of either
list
ordict
values by their entries corresponding to the given key. The returned value is a list of lists of the form[key, group]
, wherekey
is the value all elements of the listgroup
have in common.When grouping a list of lists, the
key
argument is a number representing the index of each list to look at. When grouping a list of dictionaries, thekey
argument is a string. Definitions:
 Examples:
group_by(0, [[0,0], [3,2], [0,4]])
→[[0, [[0,0], [0,4]]], [3, [[3,2]]]]
group_by("a", [["a": 1, "b": "M"], ["a": 2, "b": "S"], ["a": 1, "b": "XL"]])
→[[1,[["a": 1, "b": "M"], ["a": 1, "b": "XL"]]], [2, [["a": 2, "b": "S"]]]]

indices
(list, value)¶ Find the indices at which
value
occurs inlist
.

distinct
(x)¶ Return a copy of the list
x
with duplicates removed.

list
(x) Convert a value to a list of its components (or rows, for a matrix).
 Definitions:
 Examples:
list(set(1,2,3))
→[1,2,3]
(note that you can’t depend on the elements of sets being in any order)list(vector(1,2))
→[1,2]
list(matrix([1,2],[3,4]))
→[[1,2], [3,4]]

make_variables
(definitions)¶ Evaluate a dictionary of variable definitions and return a dictionary containing the generated values.
definitions
is a dictionary mapping variable names toexpression
values corresponding to definitions.The definitions can refer to other variables to be evaluated, or variables already defined in the current scope. Variables named in the dictionary which have already been defined will be removed before evaluation begins.
 Definitions:
dict
ofexpression
,range
→dict
 Example:
make_variables(["a": expression("random(1..5)"), "b": expression("a^2")])
→["a": 3, "b": 9]

satisfy
(names, definitions, conditions, maxRuns)¶ Each variable name in
names
should have a corresponding definition expression indefinitions
.conditions
is a list of expressions which you want to evaluate totrue
. The definitions will be evaluated repeatedly until all the conditions are satisfied, or the number of attempts is greater thanmaxRuns
. IfmaxRuns
isn’t given, it defaults to 100 attempts.Note
This function is deprecated, and retained only for backwards compatibility. Use
make_variables()
instead.

sum
(numbers)¶ Add up a list of numbers

prod
(list)¶ Multiply a list of numbers together

product
(list1, list2, ..., listN) or product(list, n)¶ Cartesian product of lists. In other words, every possible combination of choices of one value from each given list.
If one list and a number are given, then the
n
th Cartesian power of the list is returned: the Cartesian product ofn
copies of the list.

zip
(list1, list2, ..., listN)¶ Combine two (or more) lists into one  the Nth element of the output is a list containing the Nth elements of each of the input lists.

combinations
(collection, r)¶ All ordered choices of
r
elements fromcollection
, without replacement.

combinations_with_replacement
(collection, r)¶ All ordered choices of
r
elements fromcollection
, with replacement.
Dictionaries¶

dict[key]
Get the value corresponding to the given key string in the dictionary
d
.If the key is not present in the dictionary, an error will be thrown.

get
(dict, key, default)¶ Get the value corresponding to the given key string in the dictionary.
If the key is not present in the dictionary, the
default
value will be returned.

dict
(a:b, c:d, ...) 
dict
(pairs) Create a dictionary with the given keyvalue pairs. Equivalent to
[ .. ]
, except when no keyvalue pairs are given:[]
creates an empty list instead.You can alternately pass a list of pairs of the form
[key, value]
, to transform a list into a dictionary. Definitions:
 multiple
keypair
→dict
 multiple
 Examples:
dict()
dict("a": 1, "b": 2)
dict([ ["a",1], ["b",2] ])

keys
(dict)¶ A list of all of the given dictionary’s keys.

values
(dict[, keys])¶ A list of the values corresponding to each of the given dictionary’s keys.
If a list of keys is given, only the values corresponding to those keys are returned, in the same order.
Sets¶

set
(a,b,c,...) or set([elements]) Create a set with the given elements. Either pass the elements as individual arguments, or as a list.

union
(a, b)¶ Union of sets
a
andb

intersection
(a, b)¶ Intersection of sets
a
andb
, i.e. elements which are in both sets.

ab
Set minus  elements which are in a but not b
 Example:
set(1,2,3,4)  set(2,4,6)
→set(1,3)
Randomisation¶

random
(x)¶ Pick uniformly at random from a range, list, or from the given arguments.

deal
(n)¶ Get a random shuffling of the integers \([0 \dots n1]\)
Control flow¶

award
(a, b)¶ Return
a
ifb
istrue
, else return0
.

if
(p, a, b)¶ If
p
istrue
, returna
, else returnb
. Only the returned value is evaluated. Definitions:
boolean
, anything, anything → unspecified
 Example:
if(false,1,0)
→0

switch
(p1, a1, p2, a2, ..., pn, an, d)¶ Select cases. Alternating boolean expressions with values to return, with the final argument representing the default case. Only the returned value is evaluated.
 Definitions:
 multiple
boolean
,anything, anything → unspecified
 multiple
 Examples:
switch(true,1,false,0,3)
→1
switch(false,1,true,0,3)
→0
switch(false,1,false,0,3)
→3

assert
(condition, value)¶ If
condition
isfalse
, then returnvalue
, otherwise don’t evaluatevalue
and returnfalse
. This is intended for use in marking scripts, to apply marking feedback only if a condition is met. Definitions:
boolean
, anything → unspecified
 Example:
assert(studentAnswer<=0, correct("Student answer is positive"))

try
(expression, name, except)¶ Try to evaluate
expression
. If it is successfully evaluated, return the result. Otherwise, evaluateexcept
, with the error message available asname
. Definitions:
 anything,
name
, anything → unspecified
 anything,
 Examples:
try(eval(expression("x+")),err, "Error: "+err)
→"Error: Not enough arguments for operation <code>+</code>"
try(1+2,err,0)
→3
HTML¶

isnonemptyhtml
(str)¶ Does
str
represent a string of HTML containing text? Returns false for the empty string, or HTML elements with no text content.

table
(data), table(data, headers)¶ Create an HTML with cell contents defined by
data
, which should be a list of lists of data, and column headers defined by the list of stringsheaders
.

image
(url)¶ Create an HTML img element loading the image from the given URL. Images uploaded through the resources tab are stored in the relative URL resources/images/<filename>.png, where <filename> is the name of the original file.
 Definitions:
 Examples:
image('resources/images/picture.png')
image(chosenimage)
 Question using randomly chosen images.
JSON¶
JSON is a lightweight datainterchange format. Many public data sets come in JSON format; it’s a good way of encoding data in a way that is easy for both humans and computers to read and write.
For an example of how you can use JSON data in a Numbas question, see the exam Working with JSON data.

json_decode
(json)¶ Decode a JSON string into JME data types.
JSON is decoded into numbers, strings, booleans, lists, or dictionaries. To produce other data types, such as matrices or vectors, you will have to postprocess the resulting data.
Warning
The JSON value
null
is silently converted to an empty string, because JME has no “null” data type. This may change in the future. Definitions:
string
→ unspecified
 Example:
json_decode(safe(' {"a": 1, "b": [2,true,"thing"]} '))
→["a": 1, "b": [2,true,"thing"]]
Subexpressions¶

expression
(string) Parse a string as a JME expression. The expression can be substituted into other expressions, such as the answer to a mathematical expression part, or the
\simplify
LaTeX command.parse(string)
is a synonym forexpression(string)
. Definitions:
 Example:

eval
(expression, values)¶ Evaluate the given subexpression.
If
values
is given, it should be a dictionary mapping names of variables to their values. Definitions:
expression
→ unspecifiedexpression
,dict
→ unspecified
 Example:
eval(expression("1+2"))
→3
eval(expression("x+1"), ["x":1])
→2

args
(expression)¶ Returns the arguments of the toplevel operation of
expression
, as a list of subexpressions. Ifexpression
is a data type other than an operation or function, an empty list is returned.Binary operations only ever have two arguments. For example,
1+2+3
is parsed as(1+2)+3
. Definitions:
 Examples:
args(expression("f(x)"))
→[expression("x")]
args(expression("1+2+3"))
→[expression("1+2"), expression("3")]
args(expression("1"))
→[]

type
(expression)¶ Returns the name of the data type of the top token in the expression, as a string.
 Definitions:
 Examples:
type(expression("x"))
→"name"
type(expression("1"))
→"integer"
type(expression("x+1"))
→"op"
type(expression("sin(x)"))
→"function"

name
(string) Construct a
name
token with the given name.

exec
(op, arguments)¶ Returns a subexpression representing the application of the given operation to the list of arguments.
 Definitions:
op
,list
→expression
 Example:
exec(op("+"), [2,1])
→expression("2+1")
exec(op(""), [2,name("x")])
→expression("2x")

findvars
(expression)¶ Return a list of all unbound variables used in the given expression. Effectively, this is all the variables that need to be given values in order for this expression to be evaluated.
Bound variables are those defined as part of operations which also assign values to those variables, such as
map
orlet
. Definitions:
 Examples:
findvars(expression("x+1"))
→["x"]
findvars(expression("x + x*y"))
→["x","y"]
findvars(expression("map(x+2, x, [1,2,3])"))
→[]

substitute
(variables, expression)¶ Substitute the given variable values into
expression
.variables
is a dictionary mapping variable names to values. Definitions:
 Examples:
substitute(["x": 1], expression("x + y"))
→expression("1 + y")
substitute(["x": 1, "y": expression("sqrt(z+2)")], expression("x + y"))
→expression("1 + sqrt(z + 2)")

simplify
(expression, rules)¶ Apply the given simplification rules to
expression
, until no rules apply.rules
is a list of names of rules to apply, given either as a string containing a commaseparated list of names, or a list of strings.Unlike the \simplify` command in content areas, the
basic
rule is not turned on by default.See Substituting variables into displayed maths for a list of rules available.
 Definitions:
 Examples:
simplify(expression("1*x+cos(pi)"),"unitfactor")
→expression("x+cos(pi)")
simplify(expression("1*x+cos(pi)"),["basic","unitfactor","trig"])
→expression("x1")

canonical_compare
(expr1, expr2)¶ Compare expressions
a
andb
using the “canonical” ordering. Returns1
ifa
should go beforeb
,0
if they are considered “equal”, and1
ifa
should go afterb
.Expressions are examined in the following order:
 Names used: all variable names used in each expression are collected in a depthfirst search and the resulting lists are compared lexicographically.
 Data type: if
a
andb
are of different data types,op
andfunction
go first, and then they are compared using the names of their data types.  Polynomials: terms of the form
x^b
ora*x^b
, wherea
andb
are numbers andx
is a variable name, go before anything else.  Function name: if
a
andb
are both function applications, they are compared using the names of the functions. If the functions are the same, the arguments are compared. Powers, or multiples of powers, go after anything else.  Number: if
a
andb
are both numbers, the lowest number goes first. Complex numbers are compared by real part and then by imaginary part.  Elements of other data types are considered to be equal to any other value of the same data type.
 Definitions:
 anything, anything →
number
 anything, anything →
 Examples:
canonical_compare(a,b)
→1
canonical_compare(f(y),g(x))
→1
canonical_compare(f(x),g(x))
→1
canonical_compare("a","b")
→0

numerical_compare
(a, b)¶ Compare expression
a
andb
by substituting random values in for the free variables.Returns
true
ifa
andb
have exactly the same free variables, and produce the same results when evaluated against the randomly chosen values.For more control over the evaluation, see
resultsequal()
. Definitions:
 Example:
numerical_compare(expression("x^2"), expression("x*x"))
→true
numerical_compare(expression("x^2"), expression("2x"))
→false
numerical_compare(expression("x^2"), expression("y^2"))
→false
Patternmatching subexpressions¶

match
(expr, pattern, options)¶ If
expr
matchespattern
, return a dictionary of the form["match": boolean, "groups": dict]
, where"groups"
is a dictionary mapping names of matches to subexpressions.See the documentation on patternmatching mathematical expressions.
If you don’t need to use any parts of the matched expression, use
matches()
instead. Definitions:
expression
,string
→dict
expression
,string
,string
→dict
 Examples:
match(expression("x+1"),"?;a + ?;b")
→["match": true, "groups": ["a": expression("x"), "b": expression("1"), "_match": expression("x+1")]]
match(expression("sin(x)"), "?;a + ?;b")
→["match": false, "groups": dict()]
match(expression("x+1"),"1+?;a")
→["match": true, "groups": ["a": expression("x"), "_match": expression("x+1")]]

matches
(expr, pattern, options)¶ Return
true
ifexpr
matchespattern
.Use this if you’re not interested in capturing any parts of the matched expression.
 Definitions:
expression
,string
→boolean
expression
,string
,string
→boolean
 Examples:
matches(expression("x+1"),"?;a + ?;b")
→true
matches(expression("sin(x)"), "?;a + ?;b")
→false

replace
(pattern, replacement, expr)¶ Replace occurrences of
pattern
inexpr
with the expression created by substituting the matched items intoreplacement
. Definitions:
 Examples:
replace("?;x + ?;y", "x*y", expression("1+2"))
→expression("1*2")
replace("?;x + ?;y", "f(x,y)", expression("1+2+3"))
→expression("f(f(1,2),3)")
replace("0*?", "0", expression("0*sin(x) + x*0 + 2*cos(0*pi)"))
→expression("0 + 0 + 2*cos(0)")
Identifying data types¶

type
(x) Returns the name of the data type of
x
. Example:
type(1)
→"integer"

x isa type
Returns
true
ifx
is of the data typetype
.

x as type
Convert
x
to the given data type, if possible.If
x
can not be automatically converted totype
, an error is thrown. Definitions:
 anything,
string
→ given type
 anything,
 Examples:
dec(1.23) as "number"
→1.23
set(1,2,3) as "list"
→[1,2,3]

infer_variable_types
(expression)¶ Attempt to infer the types of free variables in the given expression.
There can be more than one valid assignment of types to the variables in an expression. For example, in the expression
a+a
, the variablea
can be any type which has a defined addition operation.Returns the first possible assignment of types to variables, as a dictionary mapping variable names to the name of its type. If a variable name is missing from the dictionary, the algorithm can’t establish any constraint on it.
 Definitions:
 Examples:
infer_variable_types(expression("x^2"))
→["x": "number"]
infer_variable_types(expression("union(a,b)"))
→["a": "set", "b": "set"]
infer_variable_types(expression("k*det(a)"))
→[ "k": "number", "a": "matrix" ]

infer_type
(expression)¶ Attempt to infer the type of the value produced by the given expression, which may contain free variables.
First, the types of any free variables are inferred. Then, definitions of an operations or functions in the function are chosen to match the types of their arguments.
Returns the name of the expression’s output type as a string, or
"?"
if the type can’t be determined. Definitions:
 Examples:
infer_type(expression("x+2"))
→"number"
infer_type(expression("id(n)"))
→"matrix"
infer_type(expression("random(2,true)"))
→"?"
Inspecting the evaluation scope¶

definedvariables
()¶ Returns a list containing the names of every variable defined in the current scope, as strings.
 Definitions:
 () →
list
 () →

isset
(name)¶ Returns
true
if the variable with the given name has been defined in the current scope.