Dynamically extract only certain keys from an array

Question

I need to dynamically extract only certain keys from an array.

Ex:

$array = [
        "a" => true,
        "b" => false,
        "c" => [
            0 => [
                "a" => "x",
                "b" => [
                    "x" => "Y"
                ]
            ],
            1 => [
                "a" => "x",
                "b" => [
                    "x" => "Y"
                ]
            ],
        ]
    ];

And from it I need to extract the following array, which can change:

$newArray = [
        "b" => false,
        "c" => [
            0 => [
                "b" => [
                    "x" => "Y"
                ]
            ],
            1 => [
                "b" => [
                    "x" => "Y"
                ]
            ],
        ]
    ];

So you want values that are NOT `true` or what? Why do you want `b` and `c` but not `a`? What is the logic / rule? — AbraCadaver, Oct 18 '19 at 20:39
I need to generate a report from a json data, where the user define the report fields, then I need to get only same values from json, — Conrado Lemos, Oct 18 '19 at 20:45
Still not clear, `a` is `true` but you get `b` keys from the `c` array. You won't get a good answer without explaining HOW and WHY. — AbraCadaver, Oct 18 '19 at 22:50

MatWer · Accepted Answer · 2019-10-18T21:00:36.003

this might by easy with the following recursive function:

<?php
$array = [
            "a" => true,
            "b" => false,
            "c" => [
                0 => [
                    "a" => "x",
                    "b" => [
                        "x" => "Y"
                    ]
                ],
                1 => [
                    "a" => "x",
                    "b" => [
                        "x" => "Y"
                    ]
                ],
            ]
        ];

$cleaned_array = unset_by_key($array,"a");    
$extracted_array = arrayRecursiveDiff ($array, $cleaned_array);

print_r($cleaned_array);  
print_r($extracted_array);

function unset_by_key ($arr,$nkey) {
  unset($arr[$nkey]);
  foreach ($arr as $key=>$val) {
    if (is_array($val)) {
        $arr[$key] = unset_by_key($val,$nkey);
    }
  }
  return $arr;
}

// THX TO: https://stackoverflow.com/questions/3876435/recursive-array-diff
function arrayRecursiveDiff($aArray1, $aArray2) {
  $aReturn = array();

  foreach ($aArray1 as $mKey => $mValue) {
    if (array_key_exists($mKey, $aArray2)) {
      if (is_array($mValue)) {
        $aRecursiveDiff = arrayRecursiveDiff($mValue, $aArray2[$mKey]);
        if (count($aRecursiveDiff)) { $aReturn[$mKey] = $aRecursiveDiff; }
      } else {
        if ($mValue != $aArray2[$mKey]) {
          $aReturn[$mKey] = $mValue;
        }
      }
    } else {
      $aReturn[$mKey] = $mValue;
    }
  }
  return $aReturn;
} 

?>

Sorry, I think I got it wrong, I don't want to remove the $newArray keys from the initial array, I want to get the values of these keys — Conrado Lemos, Oct 18 '19 at 20:30
that you can easly to using the array_diff function recursive ... I will update the code in 1 minute — MatWer, Oct 18 '19 at 20:58
So Coed is updated and the $extracted_array holds what you looking for — MatWer, Oct 18 '19 at 21:01
Thanks a lot, with some modifications to my array structure, it worked! — Conrado Lemos, Oct 21 '19 at 13:48

score 0 · Answer 2 · answered Oct 18 '19 at 21:12

No need for recursive functions, you can just use array_intersect_key if you only intend to select by keys first level deep:

$arr = [
    'a' => true,
    'b' => false,
    'c' => [
        [
            'a' => 'x',
            'b' => [
                'x' => 'Y'
            ]
        ],
        [
            'a' => 'x',
            'b' => [
                'x' => 'Y'
            ]
        ],
    ]
];
function getKeys(array $arr, array $keys) {
    return array_intersect_key($arr, array_fill_keys($keys, null));
}

$result = getKeys($arr, ['b', 'c']);
print_r($result);

Hope that helps,

Dynamically extract only certain keys from an array

2 Answers2