Count occurrences of unique values in a column of one 2d array

Question

I currently have the following array:

Array(
    [0] => Array
        (
            [user] => Name 1
            [group] => 1
        )
    [1] => Array
        (
            [user] => Name 2
            [group] => 1
        )
    [2] => Array
        (
            [user] => Name 3
            [group] => 2
        )
    [3] => Array
        (
            [user] => Name 4
            [group] => 2
        )
    [4] => Array
        (
            [user] => Name 5
            [group] => 3
        )
)

I am attempting to create a new array with the various group values as the key, then count how many are in each group to give the following:

Array
(
    [1] => 2
    [2] => 2
    [3] => 1
)

I have attempted to use the following, however I get undefined index warnings:

$newArr = array();
foreach ($details['user_groups'] as $key => $value) {
    $newArr[$value['user_groups']]++;
}

just to make sure, you are trying to get the group from the first array? — user745235
– user745235, Commented Apr 18, 2012 at 18:32
Yeah, so the range of groups from the first array (i.e. 1-3) as the keys of the new array and then count how many are in each group, again from the first array — lethalMango
– lethalMango, Commented Apr 18, 2012 at 18:34

Community · Accepted Answer · 2023-11-17 20:38:18Z

15

This can be done with a simple iteration:

$counts = array();
foreach ($array as $key=>$subarr) {
  // Add to the current group count if it exists
  if (isset($counts[$subarr['group']]) {
    $counts[$subarr['group']]++;
  }
  // or initialize to 1 if it doesn't exist
  else $counts[$subarr['group']] = 1;

  // Or the ternary one-liner version 
  // instead of the preceding if/else block
  $counts[$subarr['group']] = isset($counts[$subarr['group']]) ? $counts[$subarr['group']]++ : 1;
}

###Update for PHP 5.5

In PHP 5.5, which has added the array_column() function to aggregate an inner key from a 2D array, this can be simplified to:

$counts = array_count_values(array_flip(array_column($array, 'group')));

edited Nov 17, 2023 at 20:38

CommunityBot

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answered Apr 18, 2012 at 18:34

Michael Berkowski

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7 Comments

user745235 Over a year ago

$counts[$subarr['group']++];

lethalMango Over a year ago

I did try that Michael using the code I included on my question, however I get undefined index warnings.

Michael Berkowski Over a year ago

@gerep Not as you have it :) I was missing a bracket, but already fixed it.

Michael Berkowski Over a year ago

@lethalMango Did you try the current version I have there? It will not give undefined index warnings. Initially, I hit the save button before completing the if/else

lethalMango Over a year ago

Sorry I saw the first version :) Works a charm, I guessed I had missed something obvious! Thanks

|

Barmar · Accepted Answer · 2017-02-18 01:53:43Z

5

This can be done with a simple array_map function

$array = array_map(function($element){
    return $element['group'];
}, $array1);

$array2 = (array_count_values($array));

print_r($array2);

edited Feb 18, 2017 at 1:53

Barmar

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answered Dec 19, 2013 at 6:32

Vijaysinh Parmar

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3 Comments

Raham Over a year ago

Dear,@Vijaysinh Parmar where you defined $array1?

Vijaysinh Parmar Over a year ago

you can refer question array as $array1.

Raham Over a year ago

Dear @Vijaysinh Parmar thank you for such a prompt response.I used my own one but after your reply I prefer yours.Thank you

FtDRbwLXw6 · Accepted Answer · 2012-04-18 19:00:02Z

2

Your initial attempt was close. You were simply using the wrong key inside the loop:

$newArr = array();
foreach ($details['user_groups'] as $key => $value) {
        // What you were using:
        // $newArr[$value['user_groups']]++;

        // What you should be using:
        $newArr[$value['group']]++;
}

answered Apr 18, 2012 at 19:00

FtDRbwLXw6

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1 Comment

mickmackusa Over a year ago

So this was a typo question? I do not endorse snippets that generate Warnings/Notices.

mickmackusa · Accepted Answer · 2024-12-07 05:46:38Z

You only need two native function calls for this task. Isolate the desired column of data with array_column(), then count the occurrences with array_count_values(). This is the only way that I would code this task in one of my projects.

The added benefit of using array_column() is that if some of your subarrays do not contain the targeted column key, then there will be no Notice/Warning generated. If you were to use a common looping technique or array_map/array_walk() instead, you might need to write conditional checks to prevent the Notices/Warnings.

Code: (Demo)

$array = [
    ['user' => 'Name 1', 'group' => 1],
    ['user' => 'Name 2', 'group' => 1],
    ['user' => 'Name 3', 'group' => 2],
    ['user' => 'Name 4', 'group' => 2],
    ['user' => 'Name 5', 'group' => 3],
];

var_export(
    array_count_values(array_column($array, 'group'))
);

If you have a good reason to use a manual loop (such as summing the encountered values or multiplying values by a quantity before adding), just null coalesce to 0 to prevent PHP complaining about incrementing/adding-to an undeclared variable. Demo

$result = [];
foreach ($array as ['group' => $g]) {
    $result[$g] = ($result[$g] ?? 0) + 1;
}
var_export($result);

Output (from either snippet):

array (
  1 => 2,
  2 => 2,
  3 => 1,
)

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