Concat values of array with same key - php

Question

I want to concat values of array with same key
Example:
[0] => Array
(
[0] => A
[1] => XYZ
)
[1] => Array
(
[0] => B
[1] => ABC
)
[2] => Array
(
[0] => A
[1] => LMN
)
[3] => Array
(
[0] => B
[1] => PQR
)
)
Expected output:
[0] => Array
(
[0] => A
[1] => XYZ,LMN
)
[1] => Array
(
[0] => B
[1] => ABC,PQR
)
)

Answer 1

A simple solution uses the PHP function array_reduce():
// The input array you posted in the question
$input = array(
array('A', 'XYZ'),
array('B', 'ABC'),
array('A', 'LMN'),
array('B', 'PQR'),
);
// Reduce the array to a new array that contains the data aggregated as you need
$output = array_reduce(
// Process each $item from $input using a callback function
$input,
// The callback function processes $item; the partial result is $carry
function (array $carry, array $item) {
// Extract the key into a variable
$key = $item[0];
// If the key was encountered before
// then a partial entry already exists in $carry
if (isset($carry[$key])) {
// Append the desired value to the existing entry
$carry[$key][1] .= ','.$item[1];
} else {
// Create a new entry in $carry (copy $item to key $key for quick retrieval)
$carry[$key] = $item;
}
// Return the updated $carry
return $carry;
},
// Start with an empty array (it is known as $carry in the callback function)
array()
);
// $output contains the array you need

Answer 2

Try this:
$final = array();
foreach ($array_items as $item)
{
$key = $item[0];
$found_index = -1;
for ($i=0; $i<count($final); $i++)
{
if ($key == $final[$i][0])
{
$found_index = $i;
break;
}
}
if ($found_index == -1)
{
$final_item = array();
$final_item[0] = $key;
$final_item[1] = $item[1];
$final[] = $final_item;
}
else
{
$final[$found_index][1] .= ",".$item[1];
}
}
We create a new array $final, and loop through your old array $array_items. For each item, we see if there is already an item in $final that has the same [0] index. If it doesn't exist, we create it and add the initial string to the [1] index. If it does exist, we just have to add the string onto the end of the [1] index.
Try it, substituting $array_items for whatever your array is called, let me know if it works.

Answer 3

Check my solution. It should work fine. I hope it will help you much.
$result = $passed_keys = $extended_arr = [];
foreach ($arr as $k => $value) {
for($i = $k + 1; $i < count($arr); $i++){
if ( $value[0] == $arr[$i][0] ){ // compare each array with rest subsequent arrays
$key_name = $value[0];
if (!array_key_exists($key_name, $result)){
$result[$key_name] = $value[1] .",". $arr[$i][1];
} else {
if (!in_array($i, $passed_keys[$key_name])) {
$result[$key_name] .= ",". $arr[$i][1];
}
}
$passed_keys[$key_name][] = $i; // memorizing keys that were passed
}
}
}
array_walk($result, function($v, $k) use(&$extended_arr){
$extended_arr[] = [$k, $v];
});
The result is in $extended_arr

Answer 4

My solution, creates a custom key which makes identifying the letter much easier. This removes the need to continuously iterate through each array, which can become a major resources hog.
<?php
$inital_array = array(
array('A','XYZ'),
array('B','ABC'),
array('A','LMN'),
array('B','PQR')
);
$concat_array = array();
foreach($inital_array as $a){
$key = $a[0];
if( !isset($concat_array[$key]) ){
$concat_array[$key] = array($key,'');
}
$concat_array[$key][1] .= (empty($concat_array[$key][1]) ? '' : ',').$a[1];
}
$concat_array = array_values($concat_array);
echo '<pre>',print_r($concat_array),'</pre>';