created: 20190206140446821
modified: 20230321133008898
tags: Filters
title: Mathematics Operators
type: text/vnd.tiddlywiki

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

! Using mathematics operators

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

<$macrocall $name=".warning" _="Some filter operators remove duplicate items which can cause unexpected results when using the mathematics operators. See [[Dominant Append]] for details."/>

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 parameter 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]]">>
* ''Reducing 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[]]">>
** <<.inline-operator-example "=1 =2 =3 =4 +[average[]]">>


! Operations Combination

Operations can be combined by concatenating them while merging the inner `][` characters.

* <<.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>""" />

! Mathematics Operators list

<table>
<tr>
<th align="left">Operator</th>
<th align="left">Purpose</th>
</tr>
<$list filter="[tag[Mathematics Operators]sort[caption]]">
<tr>
<td><$link>{{!!caption}}</$link></td>
<td>{{!!op-purpose}}</td>
</tr>
</$list>
</table>


