How do I use array_unique on an array of arrays?
I have an array
Array(
[0] => Array
(
[0] => 33
[user_id] => 33
[1] => 3
[frame_id] => 3
)
[1] => Array
(
[0] => 33
[user_id] => 33
[1] => 3
[frame_id] => 3
)
[2] => Array
(
[0] => 33
[user_id] => 33
[1] => 8
[frame_id] => 8
)
[3] => Ar开发者_如何转开发ray
(
[0] => 33
[user_id] => 33
[1] => 3
[frame_id] => 3
)
[4] => Array
(
[0] => 33
[user_id] => 33
[1] => 3
[frame_id] => 3
)
)
As you can see key 0 is the same as 1, 3 and 4. And key 2 is different from them all.
When running the array_unique function on them, the only left is
Array (
[0] => Array
(
[0] => 33
[user_id] => 33
[1] => 3
[frame_id] => 3
)
)
Any ideas why array_unique isn't working as expected?
It's because array_unique
compares items using a string comparison. From the docs:
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 string representation of an array is simply the word Array
, no matter what its contents are.
You can do what you want to do by using the following:
$arr = array(
array('user_id' => 33, 'frame_id' => 3),
array('user_id' => 33, 'frame_id' => 3),
array('user_id' => 33, 'frame_id' => 8)
);
$arr = array_intersect_key($arr, array_unique(array_map('serialize', $arr)));
//result:
array
0 =>
array
'user_id' => int 33
'user' => int 3
2 =>
array
'user_id' => int 33
'user' => int 8
Here's how it works:
Each array item is serialized. This will be unique based on the array's contents.
The results of this are run through
array_unique
, so only arrays with unique signatures are left.array_intersect_key
will take the keys of the unique items from the map/unique function (since the source array's keys are preserved) and pull them out of your original source array.
Here's an improved version of @ryeguy's answer:
<?php
$arr = array(
array('user_id' => 33, 'tmp_id' => 3),
array('user_id' => 33, 'tmp_id' => 4),
array('user_id' => 33, 'tmp_id' => 5)
);
# $arr = array_intersect_key($arr, array_unique(array_map('serialize', $arr)));
$arr = array_intersect_key($arr, array_unique(array_map(function ($el) {
return $el['user_id'];
}, $arr)));
//result:
array
0 =>
array
'user_id' => int 33
'tmp_id' => int 3
First, it doesn't do unneeded serialization. Second, sometimes attributes may be different even so id is the same.
The trick here is that array_unique()
preserves the keys:
$ php -r 'var_dump(array_unique([1, 2, 2, 3]));'
array(3) {
[0]=>
int(1)
[1]=>
int(2)
[3]=>
int(3)
}
This let's array_intersect_key()
leave the desired elements.
I've run into it with Google Places API. I was combining results of several requests with different type of objects (think tags). But I got duplicates, since an object may be put into several categories (types). And the method with serialize
didn't work, since the attrs were different, namely, photo_reference
and reference
. Probably these are like temporary ids.
array_unique()
only supports multi-dimensional arrays in PHP 5.2.9 and higher.
Instead, you can create a hash of the array and check it for unique-ness.
$hashes = array();
foreach($array as $val) {
$hashes[md5(serialize($val))] = $val;
}
array_unique($hashes);
array_unique deosn't work recursive, so it just thinks "this are all Array
s, let's kill all but one... here we go!"
Quick Answer (TL;DR)
- Distinct values may be extracted from PHP Array of AssociativeArrays using foreach
- This is a simplistic approach
Detailed Answer
Context
- PHP 5.3
- PHP Array of AssociativeArrays (tabluar composite data variable)
- Alternate name for this composite variable is ArrayOfDictionary (AOD)
Problem
- Scenario: DeveloperMarsher has a PHP tabular composite variable
- DeveloperMarsher wishes to extract distinct values on a specific name-value pair
- In the example below, DeveloperMarsher wishes to get rows for each distinct
fname
name-value pair
Solution
example01 ;; DeveloperMarsher starts with a tabluar data variable that looks like this
$aodtable = json_decode('[ { "fname": "homer" ,"lname": "simpson" }, { "fname": "homer" ,"lname": "jackson" }, { "fname": "homer" ,"lname": "johnson" }, { "fname": "bart" ,"lname": "johnson" }, { "fname": "bart" ,"lname": "jackson" }, { "fname": "bart" ,"lname": "simpson" }, { "fname": "fred" ,"lname": "flintstone" } ]',true);
example01 ;; DeveloperMarsher can extract distinct values with a foreach loop that tracks seen values
$sgfield = 'fname'; $bgnocase = true; // $targfield = $sgfield; $ddseen = Array(); $vout = Array(); foreach ($aodtable as $datarow) { if( (boolean) $bgnocase == true ){ @$datarow[$targfield] = @strtolower($datarow[$targfield]); } if( (string) @$ddseen[ $datarow[$targfield] ] == '' ){ $rowout = array_intersect_key($datarow, array_flip(array_keys($datarow))); $ddseen[ $datarow[$targfield] ] = $datarow[$targfield]; $vout[] = Array( $rowout ); } } //;; print var_export( $vout, true );
Output result
array ( 0 => array ( 0 => array ( 'fname' => 'homer', 'lname' => 'simpson', ), ), 1 => array ( 0 => array ( 'fname' => 'bart', 'lname' => 'johnson', ), ), 2 => array ( 0 => array ( 'fname' => 'fred', 'lname' => 'flintstone', ), ), )
Pitfalls
- This solution does not aggregate on fields that are not part of the DISTINCT operation
- Arbitrary name-value pairs are returned from arbitrarily chosen distinct rows
- Arbitrary sort order of output
- Arbitrary handling of letter-case (is capital A distinct from lower-case a ?)
See also
- php array_intersect_key
- php array_flip
function array_unique_recursive($array)
{
$array = array_unique($array, SORT_REGULAR);
foreach ($array as $key => $elem) {
if (is_array($elem)) {
$array[$key] = array_unique_recursive($elem);
}
}
return $array;
}
Doesn't that do the trick ?
`
$arr = array(
array('user_id' => 33, 'tmp_id' => 3),
array('user_id' => 33, 'tmp_id' => 4),
array('user_id' => 33, 'tmp_id' => 3),
array('user_id' => 33, 'tmp_id' => 4),
);
$arr1 = array_unique($arr,SORT_REGULAR);
echo "<pre>";
print_r($arr1);
echo "</pre>";
Array(
[0] => Array(
[user_id] => 33
[tmp_id] => 3
)
[1] => Array(
[user_id] => 33
[tmp_id] => 4
)
)
`
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