created: 20190206140446821
modified: 20190206140446821
title: Mathematics Operators
tags: Filters

<<.from-version "5.1.20">>The mathematics filter operators allow numerical calculations to be performed within filters.

The mathematics operators interpret their arguments as numbers according to the following rules:

* Any non-numeric characters after a valid number are ignored (e.g. `28px` is interpreted as the number 28)
* If the argument cannot be interpreted as a number, the value 0 is used (e.g. `foo` is interpreted as the number 0)
* The special values `Infinity` and `-Infinity` can be used to represent positive and negative infinity respectively

The mathematics operators take three different forms:

* ''Unary operators'' apply an operation to each number in the input list (e.g. negate, truncate, sign)
** <<.inline-operator-example "1 2 3 4 +[negate[]]">>
** <<.inline-operator-example "1.2 2.4 3.6 4.8 +[trunc[]]">>
** <<.inline-operator-example "1.2 2.4 3.6 4.8 +[round[]]">>
* ''Binary operators'' apply an operation and operand to each number in the input list (e.g. add, multiply, remainder) 
** <<.inline-operator-example "1 2 3 4 +[add[3]]">>
** <<.inline-operator-example "1 2 3 4 +[multiply[8]]">>
* ''Array operators'' apply an operation to all of the numbers in the input list, returning a single result (e.g. sum, product)
** <<.inline-operator-example "1 2 3 4 +[sum[]]">>
** <<.inline-operator-example "1 2 3 4 +[product[]]">>

Operators can be combined:

* <<.inline-operator-example "[[355]divide[113]fixed[5]]">>
* <<.inline-operator-example "[range[100]sum[]divide[100]]">>
* <<.inline-operator-example "[tag[HelloThere]get[text]length[]sum[]]">>

Complex operations will sometimes need to be split up into separate filters. For example, to compute the average length of the text field of tiddlers tagged "~HelloThere":

<$macrocall $name='wikitext-example-without-html'
src="""<$set name="number-of-tiddlers" value={{{ [tag[HelloThere]count[]] }}}>
Average length of <$text text=<<number-of-tiddlers>>/> tiddlers tagged <<tag "HelloThere">>: <$text text={{{ [tag[HelloThere]get[text]length[]sum[]divide<number-of-tiddlers>fixed[3]] }}}/>
</$set>""" />

<<list-links "[tag[Mathematics Operators]]">>