Count unique values in a column of an array

Question

I have an array like this:

$arr = [
    1 => ['A' => '1', 'C' => 'TEMU3076746'],
    2 => ['A' => '2', 'C' => 'FCIU5412720'],
    3 => ['A' => '3', 'C' => 'TEMU3076746'],
    4 => ['A' => '4', 'C' => 'TEMU3076746'],
    5 => ['A' => '5', 'C' => 'FCIU5412720']
];

My goal is to count the distinct values in the C column of the 2-dimensional array.

The total rows in the array is found like this: count($arr) (which is 5).

How can I count the number of rows which contain a unique value in the 'C' column?

If I removed the duplicate values in the C column, there would only be: TEMU3076746 and FCIU5412720

My desired output is therefore 2.

Sahil Gulati · Answer 1 · 2017-08-31T10:42:57.077

5

Hope this simplest one will be helpful. Here we are using array_column, array_unique and count.

Try this code snippet here

echo count(
        array_unique(
                array_column($data,"C")));

Result: 2

edited Aug 31 '17 at 10:42

answered Aug 31 '17 at 09:55

Sahil Gulati

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2

Just saying, can also use `array_flip` in the place of `array_unique`. +1 – Thamilhan Aug 31 '17 at 09:59
2

that's some dark evil usage of array_flip ... as long as the values are strings or integers it works. – Jakumi Aug 31 '17 at 10:04

score 2 · Answer 2 · answered Aug 31 '17 at 09:54

combine array_map, array_unique, count

$array = [ /* your array */ ];
$count = count(
    array_unique(
        array_map(function($element) { 
            return $element['C']; 
        }, $array))))

or use array_column as suggested by sahil gulati, array_map can do more stuff which probably isn't needed here.

score 1 · Answer 3 · edited Mar 05 '18 at 12:35

1

I had a very similar need and I used a slightly different method.

I have several events where teams are participating and I need to know how many teams there are in each event. In other words, I don't need to only know how many distinct item "C" there are, but how many items TEMU3076746 and FCIU5412720 there are.

The code will then be as is

$nbCs = array_count_values ( array_column ( $array, 'C' ) );

$nbCs will issue an array of values = Array([TEMU3076746] => 3 [FCIU5412720] => 2)

See example in sandbox Sandbox code

edited Mar 05 '18 at 12:35

DIF

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answered Mar 05 '18 at 11:00

Alex Tanner

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4

This answer is 1. Doing more counting work than the task requires and 2. Does not count the generated elements. This answer would need the additional call of `count()`. – mickmackusa Oct 23 '21 at 22:33

score 0 · Answer 4 · answered Oct 23 '21 at 02:43

$data=array();
$data=[
       1 => [
             'A' => '1'
             'C' => 'TEMU3076746'
            ]

       2 => [
             'A' => '2'
             'C' => 'FCIU5412720'
            ]

       3 => [
             'A' => '3'
             'C' => 'TEMU3076746'
            ]
       
       4 => [
            'A' => '4'
            'C' => 'TEMU3076746'
            ]

       5 => [
             'A' => '5'
             'C' => 'FCIU5412720'
           ]
        ];

 $total_value=count(
    array_unique(
            array_column($data,"C")));
echo $total_value;

Please only add an answer if you have something unique and valuable to add to the page. — mickmackusa, Oct 23 '21 at 03:17

mickmackusa · Answer 5 · 2021-10-24T00:26:47.337

Most concisely, use array_column()'s special ability to assign new first level keys using the targeted column's values. This provides the desired effect of uniqueness because arrays cannot contain duplicate keys on the same level.

Code: (Demo)

echo count(array_column($arr, 'C', 'C')); // 2

To be perfectly clear, array_column($arr, 'C', 'C') produces:

array (
  'TEMU3076746' => 'TEMU3076746',
  'FCIU5412720' => 'FCIU5412720',
)

This would also work with array_column($arr, null, 'C'), but that create a larger temporary array.

p.s. There is a fringe case that may concern researchers who are seeking unique float values. Assigning new associative keys using float values is inappropriate/error-prone because the keys will lose precision (become truncated to integers).

In that fringe case with floats, fallback to the less performant technique: count(array_unique(array_column($arr, 'B))) Demo

Count unique values in a column of an array

5 Answers5