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PHP – get multiple columns from array

Posted by: admin July 12, 2020 Leave a comment

Questions:

I have this array:

0 => array:3 [
    "product_id" => "1138"
    "product_image" => "/resources/medias/shop/products/shop-6500720--1.png"
    "product_sku" => "6500722"
  ]
1 => array:3 [
    "product_id" => "1144"
    "product_image" => "/resources/medias/shop/products/shop-6501041--1.png"
    "product_sku" => "6501046"
  ]
2 => array:3 [
    "product_id" => "113"
    "product_image" => "/resources/medias/shop/products/shop-6294909--1.png"
    "product_sku" => "6294915"
]

What I am looking for is a way to get a multiple array with only required columns (array_column is not a option, since it’s give me only 1 column).

What I have done

function colsFromArray($array, $keys)
{
    return array_map(function ($el) use ($keys) {
        return array_map(function ($c) use ($el) {
            return $el[$c];
        }, $keys);
    }, $array);
}

$array = array(
    [
        "product_id"    => "1138",
        "product_image" => "/resources/medias/shop/products/shop-6500720--1.png",
        "product_sku"   => "6500722"
    ],
    [
        "product_id"    => "1144",
        "product_image" => "/resources/medias/shop/products/shop-6501041--1.png",
        "product_sku"   => "6501046"
    ],
    [
        "product_id"    => "113",
        "product_image" => "/resources/medias/shop/products/shop-6294909--1.png",
        "product_sku"   => "6294915"
    ]
);
colsFromArray($array, array("product_id", "product_sku"));

//0 => array:3 [
//    "product_id" => "1138"
//    "product_sku" => "6500722"
//  ]
//1 => array:3 [
//    "product_id" => "1144"
//    "product_sku" => "6501046"
//  ]
//2 => array:3 [
//    "product_id" => "113"
//    "product_sku" => "6294915"
//]

The problem is that it seems too laggy, since it iterates twice over this.
Is there any way to get multiple columns without this workaround?
PHP: 5.6

How to&Answers:

I think the bigger issue is you lose the keys

Original Code

array (
  0 => 
  array (
    0 => '1138',
    1 => '6500722',
  ),
  1 => 
  array (
    0 => '1144',
    1 => '6501046',
  ),
  2 => 
  array (
    0 => '113',
    1 => '6294915',
 );

You can use a simple foreach instead of the second array_map:

function colsFromArray(array $array, $keys)
{
    if (!is_array($keys)) $keys = [$keys];
    return array_map(function ($el) use ($keys) {
        $o = [];
        foreach($keys as $key){
            //  if(isset($el[$key]))$o[$key] = $el[$key]; //you can do it this way if you don't want to set a default for missing keys.
            $o[$key] = isset($el[$key])?$el[$key]:false;
        }
        return $o;
    }, $array);
}

Output

array (
  0 => 
  array (
    'product_id' => '1138',
    'product_sku' => '6500722',
  ),
  1 => 
  array (
    'product_id' => '1144',
    'product_sku' => '6501046',
  ),
  2 => 
  array (
    'product_id' => '113',
    'product_sku' => '6294915',
  ),
)

Sandbox

the problem is that it seems too laggy, since it iterates twice over this.

There is no real way to not iterate over it 2 times, but you probably don’t want to throw away the keys either.

That said you can recursively unset the items you don’t want.

function colsFromArray(array &$array, $keys)
{
    if (!is_array($keys)) $keys = [$keys];
    foreach ($array as $key => &$value) {
        if (is_array($value)) {
            colsFromArray($value, $keys); //recursive
        }else if(!in_array($key, $keys)){
           unset($array[$key]); 
        }
    }
}

colsFromArray($array, array("product_id", "product_sku"));
var_export($array);

Same output as before

This is easier to do by reference. Rather or not that is faster you’ll have to test the 2 and see.

Sandbox

As a final note you shouldn’t assume the key will exist or that keys will be an array unless you type cast it as an array.

You could also do it with array filter

function colsFromArray(array $array, $keys)
{
    if (!is_array($keys)) $keys = [$keys];
    $filter = function($k) use ($keys){
       return in_array($k,$keys);
    };
    return array_map(function ($el) use ($keys,$filter) {
        return array_filter($el, $filter, ARRAY_FILTER_USE_KEY );
    }, $array);
}

There is some small performance benefit to declaring the function for filtering outside of the loop (array_map).

Sandbox

Answer:

If you need two columns from an array where one is SKU (which generally is unique) then you can use array_column with the third parameter.

$new = array_column($arr, "product_id", "product_sku");

This will return a flat array with the SKU as the key and ID as value making the array easy to work with also.

Output:

array(3) {
  [6500722]=>
  string(4) "1138"
  [6501046]=>
  string(4) "1144"
  [6294915]=>
  string(3) "113"
}

https://3v4l.org/UDGiO

Answer:

If you do not want to change your original array and want your desired output

Use array_insersect_key function to get your desired output as following

$array = array(
    [
        "product_id"    => "1138",
        "product_image" => "/resources/medias/shop/products/shop-6500720--1.png",
        "product_sku"   => "6500722"
    ],
    [
        "product_id"    => "1144",
        "product_image" => "/resources/medias/shop/products/shop-6501041--1.png",
        "product_sku"   => "6501046"
    ],
    [
        "product_id"    => "113",
        "product_image" => "/resources/medias/shop/products/shop-6294909--1.png",
        "product_sku"   => "6294915"
    ]
);

$keys = array("product_id"=>1, "product_sku"=>2);

$filteredArray = array_map(function($a) use($keys){
    return array_intersect_key($a,$keys);
}, $array);

print_r($filteredArray);

Answer:

I refactored the elegant approach from @Chayan into a function so it can be used like array_column(). Keys to be filtered can now be presented as a simple array.

Btw this is most likely also the fastest approach, since it uses build-in functions for most of the heavy lifting.

<?php

function array_columns(array $arr, array $keysSelect)
{    
    $keys = array_flip($keysSelect);
    $filteredArray = array_map(function($a) use($keys){
        return array_intersect_key($a,$keys);
    }, $arr);

    return $filteredArray;
}

$arr = array(
    [
        "product_id"    => "1138",
        "product_image" => "/resources/medias/shop/products/shop-6500720--1.png",
        "product_sku"   => "6500722"
    ],
    [
        "product_id"    => "1144",
        "product_image" => "/resources/medias/shop/products/shop-6501041--1.png",
        "product_sku"   => "6501046"
    ],
    [
        "product_id"    => "113",
        "product_image" => "/resources/medias/shop/products/shop-6294909--1.png",
        "product_sku"   => "6294915"
    ]
);

$keysSelect = array("product_id" , "product_sku");
$filteredArray = array_colums($arr, $keysSelect);

var_dump($filteredArray);

Answer:

If I understand your question correctly, you could try a traditional foreach – it might be a little faster.

function colsFromArray($array, $filterKeys) {
    $newArr = [];
    foreach($array as $key => $val) {
       $element = [];
       foreach($filterKeys as $filterKey) {
          $element[$filterKey] = $val[$filterKey];
       }
       $newArr[] = $element;
    }
}

(Not tested)

The problem is that it seems too laggy, since it iterates twice over this

Your original code isn’t iterating twice over the same array. You won’t be able to get around iterating over the main array and then the filterKeys array if you want to have an array where each element is another array of elements with keys from the filterKeys array.

Answer:

This is a refactored function based on Chayan’s with added renaming of selected columns:


 /** Function - array_columns  Selects columns from multidimantional array and renames columns as required
 *
 * @param  array $arr, array $selectColRenameKeys 
 *            example: (NewName1->colNameneeded1,NewName2->colNameneeded2,ect...)
 * @return array
 * @access public
 * 
 */   

 private function array_columns( $arr,$selectColRenameKeys) {    
    $keys = array_flip($selectColRenameKeys);
    $filteredArray = array_map(function($a) use($keys){
                                  $data = array_intersect_key($a,$keys);
                                  $rename_arr= array();
                                  foreach ($data as $colname => $value){
                                    $r_arr[$keys[$colname]]= $value   ;
                                  }
                                  return $r_arr;
                               }, $arr);

    return $filteredArray;
}

Answer:

An added feature to the array_columns function that eventually traces back to Chayan’s answer, this time extended from Joseph Mangion’s function.

I occasionally have long lists of the selected columns where I want to preserve the keys and don’t necessarily want to follow the cumbersome ['orignal_field_name'] => ['original_field_name'] format for a great number of fields.

This version preserves the original key for each field by default unless a new key is specified.

// See answer from Joseph Mangion: https://stackoverflow.com/questions/52706383/php-get-multiple-columns-from-array
/** Function - array_columns  Selects columns from multidimensional array and renames columns as required
*
* @param  array $in_array, array $select_columns_rename_keys
*   example of $select_columns_rename_keys:
*       ['new_column_name1' => 'original_column_name1', 'original_column_name2', 'original_column_name3', 'new_column_name4' => 'original_column_name4', ...]
*       This will use the original keys for columns 2 and 3 and rename columns 1 and 4
* @return array
* @access public
* 
*/   

public function array_columns($in_array, $select_columns_rename_keys) {
    foreach ($select_columns_rename_keys as $k => $v)
        if (is_int($k)) {
            $select_columns_rename_keys[$v] = $v;
            unset($select_columns_rename_keys[$k]);
        }
    $keys = array_flip($select_columns_rename_keys);
    $filtered_array =
        array_map(function($a) use($keys) {
        $data = array_intersect_key($a, $keys);
        $return_array = [];
        foreach ($data as $column_name => $value) $return_array[$keys[$column_name]] = $value;
        return $return_array;
    }, $in_array);

    return $filtered_array;
}