---
title: List Functions
---

<% fun_fact do %>
In Sass, every [map][] counts as a list that contains a two-element list for
each key/value pair. For example, `(1: 2, 3: 4)` counts as `(1 2, 3 4)`. So all
these functions work for maps as well!

[map]: ../values/maps

Individual values also count as lists. All these functions treat `1px` as a list
that contains the value `1px`.
<% end %>


<% function 'append($list, $val, $separator: auto)', returns: 'list' do %>
Returns a copy of `$list` with `$val` added to the end.

If `$separator` is `comma`, the returned list is comma-separted. If it's
`space`, the returned list is space-separated. If it's `auto` (the default), the
returned list will use the same separator as `$list` (or `space` if `$list`
doesn't have a separator). Other values aren't allowed.

[separator]: ../values/lists

Note that unlike [`join()`](#join), if `$val` is a list it's nested within the
returned list rather than having all its elements added to the returned list.

<% example(autogen_css: false) do %>
@debug append(10px 20px, 30px); // 10px 20px 30px
@debug append((blue, red), green); // blue, red, green
@debug append(10px 20px, 30px 40px); // 10px 20px (30px 40px)
@debug append(10px, 20px, $separator: comma); // 10px, 20px
@debug append((blue, red), green, $separator: space); // blue red green
===
@debug append(10px 20px, 30px)  // 10px 20px 30px
@debug append((blue, red), green)  // blue, red, green
@debug append(10px 20px, 30px 40px)  // 10px 20px (30px 40px)
@debug append(10px, 20px, $separator: comma)  // 10px, 20px
@debug append((blue, red), green, $separator: space)  // blue red green
<% end %>
<% end %>


<% function 'index($list, $value)', returns: 'number | null' do %>
Returns the [index][] of `$value` in `$list`.

[index]: ../values/lists#indexes

If `$value` doesn't appear in `$list`, this returns [`null`][]. If `$value`
appears multiple times in `$list`, this returns the index of its first
appearance.

[index]: ../values/null

<% example(autogen_css: false) do %>
@debug index(1px solid red, 1px); // 1
@debug index(1px solid red, solid); // 2
@debug index(1px solid red, dashed); // null
===
@debug index(1px solid red, 1px)  // 1
@debug index(1px solid red, solid)  // 2
@debug index(1px solid red, dashed)  // null
<% end %>
<% end %>


<% function 'is-bracketed($list)', returns: 'boolean' do %>
Returns whether `$list` has square brackets.

<% example(autogen_css: false) do %>
@debug is-bracketed(1px 2px 3px); // false
@debug is-bracketed([1px, 2px, 3px]); // true
===
@debug is-bracketed(1px 2px 3px)  // false
@debug is-bracketed([1px, 2px, 3px])  // true
<% end %>
<% end %>


<% function 'join($list1, $list2, $separator: auto, $bracketed: auto)', returns: 'list' do %>
Returns a new list containing the elements of `$list1` followed by the elements
of `$list2`.

<% heads_up do %>
Because individual values count as single-element lists, it's possible to use
`join()` to add a value to the end of a list. However, *this is not
recommended*, since if that value is a list it will be concatenated, which is
probably not what you're expecting.

Use [`append()`](#append) instead to add a single value to a list. Only use
`join()` to combine two lists together into one.
<% end %>

If `$separator` is `comma`, the returned list is comma-separted. If it's
`space`, the returned list is space-separated. If it's `auto` (the default), the
returned list will use the same separator as `$list1` if it has a separator, or
else `$list2` if it has a separator, or else `space`. Other values aren't
allowed.

If `$bracketed` is `true`, the returned list has square brackets. If it's
`false`, the returned list has no brackets. If it's `auto` (the default), the
returned list will be bracketed if `$list1` is. Other values aren't allowed.

<% example(autogen_css: false) do %>
@debug join(10px 20px, 30px 40px); // 10px 20px 30px 40px
@debug join((blue, red), (#abc, #def)); // blue, red, #abc, #def
@debug join(10px, 20px); // 10px 20px
@debug join(10px, 20px, $separator: comma); // 10px, 20px
@debug join((blue, red), (#abc, #def), $separator: space); // blue red #abc #def
@debug join([10px], 20px); // [10px 20px]
@debug join(10px, 20px, $bracketed: true); // [10px 20px]
===
@debug join(10px 20px, 30px 40px)  // 10px 20px 30px 40px
@debug join((blue, red), (#abc, #def))  // blue, red, #abc, #def
@debug join(10px, 20px)  // 10px 20px
@debug join(10px, 20px, comma)  // 10px, 20px
@debug join((blue, red), (#abc, #def), space)  // blue red #abc #def
@debug join([10px], 20px)  // [10px 20px]
@debug join(10px, 20px, $bracketed: true)  // [10px 20px]
<% end %>
<% end %>


<% function 'length($list)', returns: 'number' do %>
Returns the length of `$list`.

This can also return the number of pairs in a map.

<% example(autogen_css: false) do %>
@debug length(10px); // 1
@debug length(10px 20px 30px); // 3
@debug length((width: 10px, height: 20px)); // 2
===
@debug length(10px)  // 1
@debug length(10px 20px 30px)  // 3
@debug length((width: 10px, height: 20px))  // 2
<% end %>
<% end %>


<% function 'list-separator($list)', returns: 'unquoted string' do %>
Returns the name of the separator used by `$list`, either `space` or `comma`.

If `$list` doesn't have a separator, returns `space`.

<% example(autogen_css: false) do %>
@debug list-separator(1px 2px 3px); // space
@debug list-separator(1px, 2px, 3px); // comma
@debug list-separator('Helvetica'); // space
@debug list-separator(()); // space
===
@debug list-separator(1px 2px 3px)  // space
@debug list-separator(1px, 2px, 3px)  // comma
@debug list-separator('Helvetica')  // space
@debug list-separator(())  // space
<% end %>
<% end %>


<% function 'nth($list, $n)' do %>
Returns the element of `$list` at [index][] `$n`.

[index]: ../values/lists#indexes

If `$n` is negative, it counts from the end of `$list`. Throws an error if there
is no element at index `$n`.

<% example(autogen_css: false) do %>
@debug nth(10px 20px 30px, 1); // 10px
@debug nth(10px 20px 30px, -1); // 30px
@debug nth((Helvetica, Arial, sans-serif), 3); // sans-serif
===
@debug nth(10px 20px 30px, 1)  // 10px
@debug nth(10px 20px 30px, -1)  // 30px
@debug nth((Helvetica, Arial, sans-serif), 3)  // sans-serif
<% end %>
<% end %>


<% function 'set-nth($list, $n, $value)', returns: 'list' do %>
Returns a copy of `$list` with the element at [index][] `$n` replaced with
`$value`.

[index]: ../values/lists#indexes

If `$n` is negative, it counts from the end of `$list`. Throws an error if there
is no existing element at index `$n`.


<% example(autogen_css: false) do %>
@debug set-nth(10px 20px 30px, 1, 2em); // 2em 20px 30px
@debug set-nth(10px 20px 30px, -1, 8em); // 10px, 20px, 8em
@debug set-nth((Helvetica, Arial, sans-serif), 3, Roboto); // Helvetica, Arial, Roboto
===
@debug set-nth(10px 20px 30px, 1, 2em); // 2em 20px 30px
@debug set-nth(10px 20px 30px, -1, 8em); // 10px, 20px, 8em
@debug set-nth((Helvetica, Arial, sans-serif), 3, Roboto); // Helvetica, Arial, Roboto
<% end %>
<% end %>


<% function 'zip($lists...)', returns: 'list' do %>
Combines every list in `$lists` into a single list of sub-lists.

Each element in the returned list contains all the elements at that position in
`$lists`. The returned list is as long as the shortest list in `$lists`.

The returned list is always comma-separated and the sub-lists are always
space-separated.

<% example(autogen_css: false) do %>
@debug zip(10px 50px 100px, short mid long); // 10px short, 50px mid, 100px long
@debug zip(10px 50px 100px, short mid); // 10px short, 50px mid
===
@debug zip(10px 50px 100px, short mid long)  // 10px short, 50px mid, 100px long
@debug zip(10px 50px 100px, short mid)  // 10px short, 50px mid
<% end %>
<% end %>