Get all values of a specific column in a multidimensional array

Question

I have a multidimensional array, that has say, x number of columns and y number of rows.

I want specifically all the values in the 3rd column.

The obvious way to go about doing this is to put this in a for loop like this

for(i=0;i<y-1;i++)
{
   $ThirdColumn[] = $array[$i][3];
}

but there is an obvious time complexity of O(n) involved here. Is there a built in way for me to simply extract each of these rows from the array without having to loop in.

For example (this does not work offcourse)

$ThirdColumn  = $array[][3]

No, any iteration of this idea, will contain at least one for loop somewhere....its unavoidable — Kylie, Jun 18 '13 at 00:54
well, that's correct, but the keys inside our specifically begin from 1. Should have made that clearer in my post — Parijat Kalia, Jun 18 '13 at 01:09
Alternatively `array_map()` and a callback retrieving the third entry each. — mario, Jun 18 '13 at 01:14

score 32 · Answer 1 · edited Jul 07 '15 at 12:04

Given a bidimensional array $channels:

$channels = array(
    array(
        'id' => 100,
        'name' => 'Direct'
    ),
    array(
        'id' => 200,
        'name' => 'Dynamic'
    )
);

A nice way is using array_map:

$_currentChannels = array_map(function ($value) {
    return  $value['name'];
}, $channels);

and if you are a potentate (php 5.5+) through array_column:

$_currentChannels = array_column($channels, 'name');

Both results in:

Array
(
    [0] => Direct
    [1] => Dynamic
)

Star guests: array_map (php4+) and array_column (php5.5+)

// array array_map ( callable $callback , array $array1 [, array $... ] )
// array array_column ( array $array , mixed $column_key [, mixed $index_key = null ] )

score 3 · Answer 2 · answered Jun 18 '13 at 07:32

Is there a built in way for me to simply extract each of these rows from the array without having to loop in.

Not yet. There will be a function soon named array_column(). However the complexity will be the same, it's just a bit more optimized because it's implemented in C and inside the PHP engine.

score 0 · Answer 3 · edited Jun 18 '13 at 07:31

0

Try this....

   foreach ($array as $val)
   {
       $thirdCol[] = $val[2];
   }

Youll endup with an array of all values from 3rd column

edited Jun 18 '13 at 07:31

hakre

193,403
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answered Jun 18 '13 at 01:01

Kylie

11,421
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2

this is off course, what I have stated in my post as the obvious way to go about doing it is by foreach looping, but thanks anyways – Parijat Kalia Jun 18 '13 at 01:08

score 0 · Answer 4 · answered Jun 18 '13 at 22:38

0

Another way to do the same would be something like $newArray = array_map( function($a) { return $a['desiredColumn']; }, $oldArray ); though I don't think it will make any significant (if any) improvement on the performance.

answered Jun 18 '13 at 22:38

Muc

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score -2 · Answer 5 · answered Jun 18 '13 at 01:04

You could try this:

$array["a"][0]=10;
$array["a"][1]=20;
$array["a"][2]=30;
$array["a"][3]=40;
$array["a"][4]=50;
$array["a"][5]=60;

$array["b"][0]="xx";
$array["b"][1]="yy";
$array["b"][2]="zz";
$array["b"][3]="aa";
$array["b"][4]="vv";
$array["b"][5]="rr";

$output = array_slice($array["b"], 0, count($array["b"]));

print_r($output);

Get all values of a specific column in a multidimensional array

5 Answers5

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