A cool example of a php closure. Say you have a multidimensional array of values, and you want to get the certain value out of it? You can use array_values, array_filter and array_map to get the value from the array using closures in php.

php-closure.php

<?php

$currency_helper = array(
	'1' => 'HRK',
	'2' => 'AUD',
	'3' => 'CAD',
	'4' => 'CZK',
	'5' => 'DKK',
	'6' => 'HUF',
	'7' => 'JPY',
	'8' => 'NOK',
	'9' => 'SEK',
	'10' => 'CHF',
	'11' => 'GBP',
	'12' => 'USD',
	'13' => 'BAM',
	'14' => 'EUR',
	'15' => 'PLN',
);
// List taken from http://hnbex.eu/api/v1/rates/daily/ on 27.2.2018.
$json = '[{"unit_value": 1, "buying_rate": "4.730403", "selling_rate": "4.758871", "currency_code": "AUD", "median_rate": "4.744637"}, {"unit_value": 1, "buying_rate": "4.756792", "selling_rate": "4.785418", "currency_code": "CAD", "median_rate": "4.771105"}, {"unit_value": 1, "buying_rate": "0.292159", "selling_rate": "0.293917", "currency_code": "CZK", "median_rate": "0.293038"}, {"unit_value": 1, "buying_rate": "0.996336", "selling_rate": "1.002332", "currency_code": "DKK", "median_rate": "0.999334"}, {"unit_value": 100, "buying_rate": "2.368373", "selling_rate": "2.382625", "currency_code": "HUF", "median_rate": "2.375499"}, {"unit_value": 100, "buying_rate": "5.636943", "selling_rate": "5.670867", "currency_code": "JPY", "median_rate": "5.653905"}, {"unit_value": 1, "buying_rate": "0.770900", "selling_rate": "0.775540", "currency_code": "NOK", "median_rate": "0.773220"}, {"unit_value": 1, "buying_rate": "0.739139", "selling_rate": "0.743587", "currency_code": "SEK", "median_rate": "0.741363"}, {"unit_value": 1, "buying_rate": "6.437749", "selling_rate": "6.476491", "currency_code": "CHF", "median_rate": "6.457120"}, {"unit_value": 1, "buying_rate": "8.450920", "selling_rate": "8.501778", "currency_code": "GBP", "median_rate": "8.476349"}, {"unit_value": 1, "buying_rate": "6.008113", "selling_rate": "6.044271", "currency_code": "USD", "median_rate": "6.026192"}, {"unit_value": 1, "buying_rate": "3.792874", "selling_rate": "3.815700", "currency_code": "BAM", "median_rate": "3.804287"}, {"unit_value": 1, "buying_rate": "7.418217", "selling_rate": "7.462861", "currency_code": "EUR", "median_rate": "7.440539"}, {"unit_value": 1, "buying_rate": "1.778608", "selling_rate": "1.789312", "currency_code": "PLN", "median_rate": "1.783960"}]';
$api_rates = json_decode( $json, true ); // Get an array of values.

$currency = $currency_helper[ 14 ]; // Get certain currency. In our case it's EUR.

$currency_rate = array_values( array_filter( array_map( function( $el ) use ( $currency ) { // Notice the use keyword.
	if ( $el['currency_code'] === $currency ) {
		return $el['median_rate'];
	}
}, $api_rates ) ) );

print_r( $currency_rate[0] ); // We got what we wanted.