The next set of array-based functions features functions that focus on entire array instead of individual elements. We present them in two sets.
The first set consists of the following functions:
$sum_of_elements = array_sum($array); $merged_array = array_merge($array1, $array2, ...); $diff_array = array_diff($array1, $array2, ...); $unique_array = array_unique($array); $reversed_array = array_reverse($array);
Let us describe these functions.
array_sum() returns the sum of all the elements present in an array. array_merge() merges two or more arrays into one single array. array_diff() extracts elements that are not common from two or more arrays. array_unique() returns a new array by removing duplicate entries. array_reverse(), as the name suggests, returns a new array that reverses the ordering of the elements present in the passed array.
We use a simple program (provided below) to illustrate the usage of these functions.
<?php
$array_tens = array(10, 20, 30);
echo "The array is: <br>";
print_r($array_tens);
$sum = array_sum($array_tens);
echo "<br>The sum of array is $sum <br>";
$array_fives = array(15, 25, 5);
$array_new = array_merge($array_tens, $array_fives);
sort($array_new);
echo "<br>After merging, the new array is: <br>";
print_r($array_new);
$array_userid1 = array("jfulton", "tkipling", "ksimon", "hjones", "amoore");
$array_userid2 = array("jfulton", "tkipling", "ksimon");
$array_difference = array_diff($array_userid1, $array_userid2);
echo "<br><br>After diff, the new array is: <br>";
print_r($array_difference);
$array_userid_dup = array("jfulton", "tkipling", "jfulton", "msimpson", "jfulton");
$array_unique_ones = array_unique($array_userid_dup);
echo "<br><br>After unique, the new array is: <br>";
print_r($array_unique_ones);
?>
Here is the output:
The array is: Array ( [0] => 10 [1] => 20 [2] => 30 ) The sum of array is 60 After merging, the new array is: Array ( [0] => 5 [1] => 10 [2] => 15 [3] => 20 [4] => 25 [5] => 30 ) After diff, the new array is: Array ( [3] => hjones [4] => amoore ) After unique, the new array is: Array ( [0] => jfulton [1] => tkipling [3] => msimpson )
The second set presents three additional functions that work on the entire array but accept a user provided callback function. We begin with their signatures:
$filtered_array = array_filter($array, 'user_defined_function'); array_walk($array, 'user_defined_function'); $total_value = array_reduce($array, 'user_defined_function');
array_filter() filters elements from an array based on a rule (usually provided as a user defined function). array_walk() applies a given rule (or function) to all elements of the array. Due to this, array_walk() can be a very handy function when we need to apply one common rule to all the elements (e.g. checking if the element has a particular value or not). array_reduce() allows us to get a cumulative value (for example, sum) of all the elements present in an array.
We provide an example that shows usage of array_filter(). In this program, for array_filter(), we pass "divisible_by_15" as the callback function. This function returns 1 (true) if the value is divisible by 15. And, only those entries are placed into the new array ($array_filtered) for which the callback returns true.
<?php
/* Callback function */
function divisible_by_15 ($temp_var) {
if ( ($temp_var % 15) == 0 ) return 1;
return 0;
}
$array_new = array(5, 10, 15, 20, 25, 30);
$array_filtered = array_filter($array_new, 'divisible_by_15');
echo "<br><br>After filtering, the new array is: <br>";
print_r($array_filtered);
?>
Here is the output:
The array is: Array ( [0] => 5 [1] => 10 [2] => 15 [3] => 20 [4] => 25 [5] => 30 ) After filtering, the new array is: Array ( [2] => 15 [5] => 30 )
Our last example demonstrates the usage of array_walk() and array_reduce(). The examples uses "length_userid" as callback function for array_walk() and "return_length_userid" as callback function for array_reduce().
<?php
function length_userid ($var_userid) {
$var_length = strlen($var_userid);
echo "The length of userid $var_userid is $var_length <br>";
}
function return_length_userid ($sum_so_far, $var_userid) {
$local_sum = $sum_so_far + strlen($var_userid);
echo "The sum_so_far is $local_sum <br>";
return $local_sum;
}
$array_userid = array("jfulton", "tkipling", "ksimon", "msimpson", "hjones", "amoore");
echo "Doing a walk on array: <br>";
array_walk($array_userid, 'length_userid');
echo "<br>Doing a reduce on array: <br>";
$sum_strlen_userids = array_reduce($array_userid, 'return_length_userid');
echo "The total string length of all userids is is $sum_strlen_userids <br>";
?>
The output (provided below) confirms that array_walk() passes each element of the $array_userid to function "length_userid". Next, array_reduce() uses values returned for each element, and adds them up; finally, it returns the total summation. Please note the usage of "$sum_so_far" variable that gets automatically passed to return_length_userid() function called from array_reduce().
Doing a walk on array: The length of userid jfulton is 7 The length of userid tkipling is 8 The length of userid ksimon is 6 The length of userid msimpson is 8 The length of userid hjones is 6 The length of userid amoore is 6 Doing a reduce on array: The sum_so_far is 7 The sum_so_far is 15 The sum_so_far is 21 The sum_so_far is 29 The sum_so_far is 35 The sum_so_far is 41 The total string length of all userids is is 41