bazel-lib/docs/lists.md

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Functions for lists

<a id="every"></a>

## every

<pre>
every(<a href="#every-f">f</a>, <a href="#every-arr">arr</a>)
</pre>

Check if every item of `arr` passes function `f`.

Example:
  `every(lambda i: i.endswith(".js"), ["app.js", "lib.js"]) // True`


**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="every-f"></a>f |  Function to execute on every item   |  none |
| <a id="every-arr"></a>arr |  List to iterate over   |  none |

**RETURNS**

True or False


<a id="filter"></a>

## filter

<pre>
filter(<a href="#filter-f">f</a>, <a href="#filter-arr">arr</a>)
</pre>

Filter a list `arr` by applying a function `f` to each item.

Example:
  `filter(lambda i: i.endswith(".js"), ["app.ts", "app.js", "lib.ts", "lib.js"]) // ["app.js", "lib.js"]`


**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="filter-f"></a>f |  Function to execute on every item   |  none |
| <a id="filter-arr"></a>arr |  List to iterate over   |  none |

**RETURNS**

A new list containing items that passed the filter function.


<a id="find"></a>

## find

<pre>
find(<a href="#find-f">f</a>, <a href="#find-arr">arr</a>)
</pre>

Find a particular item from list `arr` by a given function `f`.

Unlike `pick`, the `find` method returns a tuple of the index and the value of first item passing by `f`.
Furthermore `find` does not fail if no item passes `f`.
In this case `(-1, None)` is returned.


**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="find-f"></a>f |  Function to execute on every item   |  none |
| <a id="find-arr"></a>arr |  List to iterate over   |  none |

**RETURNS**

Tuple (index, item)


<a id="map"></a>

## map

<pre>
map(<a href="#map-f">f</a>, <a href="#map-arr">arr</a>)
</pre>

Apply a function `f` with each item of `arr` and return a new list.

Example:
  `map(lambda i: i*2, [1, 2, 3]) // [2, 4, 6]`


**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="map-f"></a>f |  Function to execute on every item   |  none |
| <a id="map-arr"></a>arr |  List to iterate over   |  none |

**RETURNS**

A new list with all mapped items.


<a id="once"></a>

## once

<pre>
once(<a href="#once-f">f</a>, <a href="#once-arr">arr</a>)
</pre>

Check if exactly one item in list `arr` passes the given function `f`.

**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="once-f"></a>f |  Function to execute on every item   |  none |
| <a id="once-arr"></a>arr |  List to iterate over   |  none |

**RETURNS**

True or False


<a id="pick"></a>

## pick

<pre>
pick(<a href="#pick-f">f</a>, <a href="#pick-arr">arr</a>)
</pre>

Pick a particular item in list `arr` by a given function `f`.

Unlike `filter`, the `pick` method returns the first item _found_ by `f`.
If no item has passed `f`, the function will _fail_.


**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="pick-f"></a>f |  Function to execute on every item   |  none |
| <a id="pick-arr"></a>arr |  List to iterate over   |  none |

**RETURNS**

item


<a id="some"></a>

## some

<pre>
some(<a href="#some-f">f</a>, <a href="#some-arr">arr</a>)
</pre>

Check if at least one item of `arr` passes function `f`.

Example:
  `some(lambda i: i.endswith(".js"), ["app.js", "lib.ts"]) // True`


**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="some-f"></a>f |  Function to execute on every item   |  none |
| <a id="some-arr"></a>arr |  List to iterate over   |  none |

**RETURNS**

True or False


<a id="unique"></a>

## unique

<pre>
unique(<a href="#unique-arr">arr</a>)
</pre>

Return a new list with unique items in it.

Example:
  `unique(["foo", "bar", "foo", "baz"]) // ["foo", "bar", "baz"]`


**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="unique-arr"></a>arr |  List to iterate over   |  none |

**RETURNS**

A new list with unique items