I try to make some operations with JSON files.

For example I intend to subtract them. But the problem is there can be different key elements.

         $a1=[
            {"cat":2,"total":1},
            {"cat":11,"total":23},
            {"cat":13,"total":30}
        ];

        $a2=[
            {"cat":2,"total":15},
            {"cat":11,"total":13},
            {"cat":15,"total":70},
            {"cat":16,"total":40}
        ];

and result must be

        $result=[
            {"cat":2,"total":14},
            {"cat":11,"total":-10},
            {"cat":13,"total":-30},
            {"cat":15,"total":70},
            {"cat":16,"total":40}
        ]

I have tried to take elements in a loop but I could not.

would you please show me the way to make this work ?

CodePudding user response：

First, the code:

<?php

$json1 = '[{"cat":2,"total":1},{"cat":11,"total":23},{"cat":13,"total":30}]';
$json2 = '[{"cat":2,"total":15},{"cat":11,"total":13},{"cat":15,"total":70},{"cat":16,"total":40}]';

$first = json_decode($json1, true);
$second = json_decode($json2, true);

$difference = [];

foreach ($second as $s) {
    $key = null;
    $f = array_filter($first, function($v, $k) use ($s, &$key){
        $result = $v["cat"] === $s["cat"];
        if ($result) $key = $k;
        return $result;
    }, ARRAY_FILTER_USE_BOTH);
    $total = $s["total"] - (count($f) ? $f[$key]["total"] : 0);
    $difference[]=["cat" => $s["cat"], "total" => $total];
}

foreach ($first as $f) {
    $s = array_filter($second, function($v, $k) use ($f) {
        return $v["cat"] === $f["cat"];
    }, ARRAY_FILTER_USE_BOTH);
    if (!count($s)) {
        $difference[]=["cat" => $f["cat"], $total => -$f["total"]];
    }
}

echo var_dump($difference); //I tested by echoing it out

Explanation:

• I initialize two variables with the JSON inputs you have defined
• I decode them both using json_decode and I set the second parameter to true to make sure they will be associative arrays
• I loop the second
  • I initialize the key with null
  • I search for a match in the first using $s and $key so I will see these variables in the closure of the function
    • If I find such a match then I initialize $key with it
  • I subtract the first total (if exists) from the total
  • I add a new item with the matching category and the correct new total
• I loop the first
  • I search a match in the second using $f
• If no matches were found, I add the item with the matching category and negative total

In short, I loop the second and subtract the matching first if they exist, defaulting to 0 and then I loop the first to add the elements that do not have a match in the second.