Merge associative arrays by partial key match

Question

I have an array:

$a = [
    "g41" => 1,
    "g44" => 2,
    "g53" => 3
];

And another array is:

$list = [
    40,
    41,
    44,
    46,
    53
];

How to combine these arrays by partial key matches to produce the following results?

$result = [
    "41" => 1,
    "44" => 2,
    "53" => 3,
    "40" => null,
    "46" => null
];

Answer 1

since you want to the result sequence follow $a, you may need to unset $list, and push remaining lists to $result

sample code as below:

<?php

$a=["g41"=>1,"g44"=>2,"g53"=>3];

$list=[40,41,44,46,53];

$result =[];

foreach($a as $key => $value){
  $new_key = substr($key,1); //remove first character, if only you first key always single char, else you may use your own method to extract key
  if(in_array($new_key,$list)){
    $result[$new_key] = $value;
    unset($list[array_search($new_key, $list)]);//remove used key
  }
}

//push remaining as null
foreach($list as $v){
  $result[$v] = null;
}

print_r($result);

Answer 2

write your custom script

$result = [];
foreach($a as $key => $value) $result[trim($key, 'g')] = $value;
foreach($list as $key) if (!isset($result[strval($key)]) $result[strval($key)] = null;

Answer 3

Iterate $list array and check for the key in the other $a array:

$a = array("g41" => 1, "g44" => 2, "g53" => 3);
$list = array(40, 41, 44, 46, 53);

$result = [];
foreach ($list as $key) {
    $result[$key] = $a["g$key"] ?? null;
}

var_dump($result);

Output:

array(5) {
  [40]=> NULL
  [41]=> int(1)
  [44]=> int(2)
  [46]=> NULL
  [53]=> int(3)
}

Answer 4

It looks like what you want to do first is transform the keys in array $a. Then use your $list of keys to populate null values where none are present in $a.

$aKeys = preg_replace('/\D/', '', array_keys($a));
$a = array_combine($aKeys, $a);
$defaultList = array_fill_keys($list, null);
$list = array_merge($defaultList, $a);

Answer 5

1. Loop the $list array
2. Check if the list value (prepended with g) exists in the $a array. If so, push it with the desired numeric key into the result array; if not, push it into an alternative array with the desired numeric key and the default value of null.
3. When finished iterating, append the data from the alternative array to the result array.

This will properly filter your data, apply the expected default values and sort the output exactly as requested.

Code: (Demo)

foreach ($list as $v) {
    if (isset($a["g$v"])) {
        $result[$v] = $a["g$v"];
    } else {
        $extra[$v] = null;
    }
}
var_export(
    array_replace($result ?? [], $extra ?? [])
);

I am using ?? [] to fallback to an empty array in case either of the arrays are never declared (never receive any elements).