Iterator Column Extraction ViewHelper

Implementation of array_column for Fluid.

Accepts an input iterator/array and creates a new array using values from one column and optionally keys from another column.

Usage examples

<!-- Given input array of user data arrays with "name" and "uid" column: -->
<f:for each="{users -> v:iterator.column(columnKey: 'name', indexKey: 'uid')}" as="username" key="uid">
    User {username} has UID {uid}.
</f:for>

The above demonstrates the logic of the ViewHelper, but the example itself of course gives the same result as just iterating the users variable itself and outputting {user.username} etc., but the real power of the ViewHelper comes when using it to feed other ViewHelpers with data sets:

<!--
Given same input array as above. Idea being that *any* iterator
can be supported as input for "options".
-->
Select user: <f:form.select options="{users -> v:iterator.column(columnKey: 'name', indexKey: 'uid')}" />

<!-- Given same input array as above. Idea being to output all user UIDs as CSV -->
All UIDs: {users -> v:iterator.column(columnKey: 'uid') -> v:iterator.implode()}

<!-- Given same input array as above. Idea being to output all unique users' countries as a list: -->
Our users live in the following countries:
{users -> v:iterator.column(columnKey: 'countryName')
    -> v:iterator.unique()
    -> v:iterator.implode(glue: ' - ')}

Note that the ViewHelper also supports the "as" argument which allows you to not return the new array but instead assign it as a new template variable - like any other "as"-capable ViewHelper.

Caveat

This ViewHelper passes the subject directly to array_column and as such it does not support dotted paths in either key argument to extract sub-properties. That means it does not support Extbase enties as input unless you explicitly implemented ArrayAccess on the model of the entity and even then support is limited to first level properties' values without dots in their names.