Get a subset of an array based on an array of keys

Question

I wrote this function to get a subset of an array. Does php have a built in function for this. I can\'t find one in the docs. Seems like a waste if I\'m reinventing the whee

Answer 1

There is no direct function I think in PHP to get a subset from an array1 with compare to another array2 where the values are the list of key name which we fetch.

Like: array_only($array1, 'field1','field2');

But this way can be achieved the same.

<?php

$associative_array = ['firstname' => 'John', 'lastname' => 'Smith', 'DOB' => '2000-10-10', 'country' => 'Ireland' ];

$subset = array_intersect_key( $associative_array, array_flip( [ 'lastname', 'country' ] ) );

print_r( $subset );

// Outputs...
// Array ( [lastname] => Smith [country] => Ireland );

Answer 2

I always want this too. Like a PHP version of Underscore's pick.

It's ugly and counter-intuitive, but what I sometimes do is this (I think this may be what prodigitalson was getting at):

$a = ['foo'=>'bar', 'zam'=>'baz', 'zoo'=>'doo'];

// Extract foo and zoo but not zam
print_r(array_intersect_key($a, array_flip(['foo', 'zoo'])));
/*
Array
(
    [foo] => bar
    [zoo] => doo
)
*/

array_intersect_key returns all the elements of the first argument whose keys are present in the 2nd argument (and all subsequent arguments, if any). But, since it compares keys to keys, I use array_flip for convenience. I could also have just used ['foo' => null, 'zoo' => null] but that's even uglier.

Answer 3

array_diff_key and array_intersect_key are probably what you want.