remove duplicates from array (array unic by key) [duplicate] - php

Question

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Filter/Remove rows where column value is found more than once in a multidimensional array
(4 answers)
Closed 3 months ago.
Array
(
[0] => Array
(
[file] => /var/websites/example.com/assets/images/200px/1419050406e6648e1c766551a0ffc91380fd6ff3406002011-10-233750.jpg
[md5] => 42479bee7a304d2318250de2ef1962a9
[url] => http://example.com/assets/images/200px/1419050406e6648e1c766551a0ffc91380fd6ff3406002011-10-233750.jpg
)
[1] => Array
(
[file] => /var/websites/example.com/assets/images/200px/21277792606e6648e1c766551a0ffc91380fd6ff3406002011-10-233750.jpg
[md5] => 42479bee7a304d2318250de2ef1962a9
[url] => http://example.com/assets/images/200px/21277792606e6648e1c766551a0ffc91380fd6ff3406002011-10-233750.jpg
)
)
How can I remove md5 key duplicates from above array?

Answer 1

<?php
$data = array(
array(
'md5' => 'alpha',
'some' => 'value',
),
array(
'md5' => 'alpha',
'some' => 'other value',
),
array(
'md5' => 'bravo',
'some' => 'third value',
),
);
// walk input array
$_data = array();
foreach ($data as $v) {
if (isset($_data[$v['md5']])) {
// found duplicate
continue;
}
// remember unique item
$_data[$v['md5']] = $v;
}
// if you need a zero-based array, otheriwse work with $_data
$data = array_values($_data);

Answer 2

PHP does already have a function to remove duplicate elements from an array. But unfortunately, array_unique does only support string based comparisons:
Note: Two elements are considered equal if and only if (string) $elem1 === (string) $elem2. In words: when the string representation is the same. The first element will be used.
The problem is that any array turned into a string is equal to any other array:
Arrays are always converted to the string "Array"; […]
But you can use the uniqueness of array keys to solve this:
$index = array();
foreach ($arr as $key => $item) {
if (isset($index[$item['md5']])) {
unset($item[$key]);
}
$index[$item['md5']] = TRUE;
}

Answer 3

Here is my final function after your help guys.... Hope it helps somebody in the future...
$data = array(
array(
'md5' => 'alpha',
'some' => 'value',
),
array(
'md5' => 'alpha',
'some' => 'other value',
),
array(
'md5' => 'bravo',
'some' => 'third value',
),
);
// walk input array
function remove_duplicateKeys($key,$data){
$_data = array();
foreach ($data as $v) {
if (isset($_data[$v[$key]])) {
// found duplicate
continue;
}
// remember unique item
$_data[$v[$key]] = $v;
}
// if you need a zero-based array
// otherwise work with $_data
$data = array_values($_data);
return $data;
}
$my_array = remove_duplicateKeys("md5",$data);

Answer 4

As array_unique operates on flat arrays, you can not use it directly. But you can first map all 'md5' values to a flat array, unique it and then get the elements with array_intersect_key:
$allMd5s = array_map(function($v) {return $v['md5'];}, $array);
$uniqueMd5s = array_unique($md5);
$result = array_intersect_key($arr, $uniqueMd5s);

Answer 5

Use array_filter(). Quick code test (doesn't necessarily mirror your situation, but you should get the idea):
<?php
header('Content-Type: Text/Plain');
$array = array(
0 => array('name' => 'samson'),
1 => array('name' => 'delilah'),
2 => array('name' => 'samson'),
3 => array('name' => 'goliath'),
);
$md5Processed = array();
$newArray = array_filter($array, "uniqueMD5");
print_r($newArray);
exit;
function uniqueMD5( $data ){
global $md5Processed;
if( !in_array( $data['name'], $md5Processed ) )
{
$md5Processed[] = $data['name'];
return true;
}
}

Answer 6

// your array
$array = array(...);
// will be used to store md5 hashes
$md5 = array();
// walk through array
foreach ($array as $key => $arr) {
// have we already seen this md5 hash?
if (in_array($arr['md5'], $md5)){
// remove element
unset($array[$key]);
}else {
// keep element, but add it's md5
$md5[] = $arr['md5'];
}
}

Answer 7

Tldr.: The obligatory one-liner:
$out = array_values ( array_intersect_key( $in, array_unique( array_column( $in, 'md5' ) ) ) );
And step by step (with my own example):
$in = [
[ 'k' => 'a' ],
[ 'k' => 'a' ],
[ 'k' => 'b' ]
];
print_r( array_column( $in, 'k' ) );
array_column returns a flat array, only with the values from all 'k'-keys:
Array
(
[0] => a
[1] => a
[2] => b
)
We can now filter that with array_unique:
print_r( array_unique( array_column( $in, 'k' ) ) ) );
To get:
Array
(
[0] => a
[2] => b
)
See that we kept the keys of the original array (0 and 2)?
We can use that with array_intersect_key. It computes the intersection of arrays using keys for comparison.
print_r( array_intersect_key( $in, array_unique( array_column( $in, 'k' ) ) ) );
We get the first [0] and third [2] entry of our original array.
Array
(
[0] => Array
(
[k] => a
)
[2] => Array
(
[k] => b
)
)
Now the keys are messed up (which might lead to problems if for loops), so we wrap the whole thing in array_values:
print_r(
array_values( array_intersect_key( $in, array_unique( array_column( $in, 'k' ) ) ) )
);
Array
(
[0] => Array
(
[k] => a
)
[1] => Array
(
[k] => b
)
)

Answer 8

Take a look at the function array_unique.