Analysis of the relationship between Array_map and Array_column in PHP _php skills

In this paper, the relationship between Array_map and Array_column in PHP is analyzed, and the detailed analysis is as follows:

The use of Array_map () and Array_column () is as follows:

Array_map (); function The callback function on the cell of the given array
Array_column () Fast implementation: converting two-dimensional arrays into one-dimensional arrays

The Array_column () function is in the following format:

Array Array_column (array $input, mixed $column _key [, Mixed $index _key]);

Returns the column whose value is column_key in the input array; If an optional parameter index_key is specified, the corresponding key in the returned array is the value index_key the input array value.

Sample code One:

$records = Array (
  array (
    ' id ' => 2135,
    ' first_name ' => ' John ',
    ' last_name ' => ' Doe '
  ),
  Array (
    ' id ' => 3245,
    ' first_name ' => ' Sally ',
    ' last_name ' => ' Smith ',
  ),
  Array (
    ' id ' => 5342,
    ' first_name ' => ' Jane ',
    ' last_name ' => ' Jones ',
  ),
  array (
    ' id ' => 5623,
    ' first_name ' => ' Peter ',
    ' last_name ' => ' Doe ',
  )
;
 
$first _names = Array_column ($records, ' first_name ');
Print_r ($first _names);

Output:

Array
(
  [0] => John
  [1] => Sally
  [2] => Jane
  [3] => Peter
)

Example code two:

$last _names = Array_column ($records, ' last_name ', ' id ');
Print_r ($last _names);

Output:

Array
(
  [2135] => doe
  [3245] => Smith
  [5342] => Jones
  [5623] => Doe
)

When there is no array_column () function,

Use Array_map () to implement example one:

$a = Array_map (function ($element) {//$records incoming callback function as a parameter return
$element [' last_name '];　　　　　　　　　　　　Returns the last_name corresponding value of an array element value
}, $records); Array_map returns an array, which is equivalent to storing each $element[' last_name ' in a new array, so the new index

Use foreach to implement example one:

foreach ($records as $v)
{
  $b [] = $v [' last_name '];
}

Use the Foreach implementation example two:
$c = Array ();
foreach ($records as $k => $v)
{
$c + + array ($v [' id ']=> $v [' last_name ']);//Use the + operator, in the form of an append (without altering the original array index), Merge assembled array
}//If using Array_merge, numeric key names are renumbered

In many of the data taken out, a typical two-dimensional array, if you need to use a single value in the data corresponding to the case, Array_column () can be completed, but in the face of a more complex array structure, foreach can make you more flexible, but priority to use system functions are always preferred.