PHP Exercises: Group the elements of an array based on the given function

PHP: Exercise-83 with Solution

Write a PHP program to group the elements of an array based on the given function.

Sample Solution: -

PHP Code:

// License: https://bit.ly/2CFA5XY
function groupBy($items, $func)
    $group = [];
    foreach ($items as $item) {
        if ((!is_string($func) && is_callable($func)) || function_exists($func)) {
            $key = call_user_func($func, $item);
            $group[$key][] = $item;
        } elseif (is_object($item)) {
            $group[$item->{$func}][] = $item;
        } elseif (isset($item[$func])) {
            $group[$item[$func]][] = $item;
    return $group;
print_r(groupBy(['one', 'two', 'three', 'four'], 'strlen'));


Sample Output:

    [3] => Array
            [0] => one
            [1] => two

    [5] => Array
            [0] => three

    [4] => Array
            [0] => four



Flowchart: Group the elements of an array based on the given function.

PHP Code Editor:

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Previous: Write a PHP program to get the index of the last element for which the given function returns a truth value.
Next: Write a PHP program to check a flat list for duplicate values. Returns true if duplicate values exists and false if values are all unique.

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PHP: Tips of the Day

Why shouldn't I use mysql_* functions in PHP?

The MySQL extension:

  • Is not under active development
  • Is officially deprecated as of PHP 5.5 (released June 2013).
  • Has been removed entirely as of PHP 7.0 (released December 2015)
  • This means that as of 31 Dec 2018 it does not exist in any supported version of PHP. If you are using a version of PHP which supports it, you are using a version which doesn't get security problems fixed.
  • Lacks an OO interface
  • Doesn't support:
    • Non-blocking, asynchronous queries
    • Prepared statements or parameterized queries
    • Stored procedures
    • Multiple Statements
    • Transactions
    • The "new" password authentication method (on by default in MySQL 5.6; required in 5.7)
    • Any of the new functionality in MySQL 5.1 or later

Since it is deprecated, using it makes your code less future proof.

Lack of support for prepared statements is particularly important as they provide a clearer, less error-prone method of escaping and quoting external data than manually escaping it with a separate function call.

Ref : https://bit.ly/2BIIsF0