PHP Exercises: Get the index of the last element for which the given function returns a truth value

Last update on April 19 2025 11:49:15 (UTC/GMT +8 hours)

82. Index of Last Element Matching a Condition

Write a PHP program to get the index of the last element for which the given function returns a truth value.

Sample Solution:

PHP Code:

<?php
// Function definition for 'find_last_Index' that takes an array of items and a filtering function as parameters
function find_last_Index($items, $func)
{
    // Use 'array_filter' to filter the items based on the given function and retrieve the keys of the filtered items
    $keys = array_keys(array_filter($items, $func));

    // Use 'array_pop' to retrieve and return the last key from the array of filtered keys
    return array_pop($keys);
}

// Call 'find_last_Index' with an array and an anonymous function checking for odd numbers, then display the result using 'echo'
echo find_last_Index([1, 2, 3, 4], function ($n) {
    return ($n % 2) === 1;
});

// Display a newline
echo "\n";

// Call 'find_last_Index' with an array and an anonymous function checking for even numbers, then display the result using 'echo'
echo find_last_Index([1, 2, 3, 4], function ($n) {
    return ($n % 2) === 0;
});

?>

Explanation:

Define find_last_Index Function:

The function find_last_Index accepts:

$items: an array of items to search through.
$func: a filtering function used to determine which items to include.

Filter Array and Retrieve Keys:

array_filter($items, $func): Filters $items based on the condition defined in $func.
array_keys(...): Retrieves the keys (indices) of the filtered items.

Return the Last Key:

array_pop($keys): Removes and returns the last key from the filtered keys array, which corresponds to the last item in $items that met the condition.

Function Calls and Output:

find_last_Index([1, 2, 3, 4], function ($n) { return ($n % 2) === 1; }):

Filters for odd numbers, returns 2, the index of the last odd number (3).

find_last_Index([1, 2, 3, 4], function ($n) { return ($n % 2) === 0; }):

Filters for even numbers, returns 3, the index of the last even number (4).

Purpose:

The function find_last_Index provides a way to find and return the index of the last element in an array that meets a specified condition, enabling flexible data retrieval based on custom criteria.

Output:

2
3

Flowchart:

For more Practice: Solve these Related Problems:

Write a PHP script to iterate backward through an array and return the index of the first element that satisfies a given condition.
Write a PHP function to determine the array key of the last element meeting a specific predicate using reverse traversal.
Write a PHP script to search an array in reverse order and output the index of the last matching element.
Write a PHP script to compute and display the key of the final element in a list that fulfills a callback condition.

PHP Code Editor:

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