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Re-key Your PHP Array with array_reduce

How much PHP code is dedicated to looping through an array of arrays (rows), comparing a search value against each row’s “column” of that name? Tons. What about re-indexing the array using the search column, so we can directly access the rows by search value?

Here’s a reducing function:

function keyBy ($reduced, $row) {
    $keyname = $reduced ['key'];
    $reduced ['data'] [$row [$keyname]] = $row;
    return $reduced;

The most important thing to keep in mind is the desire to obtain one value accumulated from an array. Inside keyBy, $reduced holds that value. The reduction works by accepting the currently reduced value and returning it with any updates you want. keyBy is extremely powerful because it will let me re-index an array of arrays using any column. Since an initial value for $reduced is required, I decided to make use of that argument to pass an arbitrary key name. To prevent any clashes with the data keys, I separated ‘key’ from ‘data’ in $reduced.

To “reduce” an array of rows into a direct-access array, I call keyBy by passing it to array_reduce, with the initial argument indicating which key to index by.

$customers = array (
	array ('id'    => 121, 'first' => 'Jane',	'last'  => 'Refrain'),
	array ('id'    => 290, 'first' => 'Bill',	'last'  => 'Swizzle'),
	array ('id'    => 001, 'first' => 'Fred',	'last'  => 'Founder')

$customersByLastName = array_reduce ($customers, "keyBy", array ('key' => 'last'));

print_r ($customersByLastName);
print $customersByLastName ['data']['Founder']['first'];

Array (
  [key] => last
  [data] => Array (
    [Refrain] => Array (
      [id] => 121
      [first] => Jane
      [last] => Refrain)

    [Swizzle] => Array (
      [id] => 290
      [first] => Bill
      [last] => Swizzle)

    [Founder] => Array (
      [id] => 1
      [first] => Fred
      [last] => Founder)


Isn’t that an incredibly small amount of code that gets rid of a lot of code? If the array is searched more than once, it quickly becomes extremely efficient.

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