PHP array
last modified January 10, 2023
In this article we show how to work with arrays in PHP.
$ php -v php -v PHP 8.1.2 (cli) (built: Aug 8 2022 07:28:23) (NTS) ...
We use PHP version 8.1.2.
PHP array definition
Arrays are collections of data. A variable can hold only one item at a time. Arrays can hold multiple items.
PHP has plenty of functions to modify, sort, merge, slice, shuffle the data inside the arrays. There are specific database handling functions for populating arrays from database queries. Several other functions return arrays.
PHP array initialization
Arrays can be initialized with a pair of [] brackets of with the
array function.
<?php $names = ["Jane", "Lucy", "Timea", "Beky", "Lenka"]; print_r($names);
We create a $names array, which stores five female names.
The print_r function prints a human readable information
about the variable.
$ php init1.php
Array
(
[0] => Jane
[1] => Lucy
[2] => Timea
[3] => Beky
[4] => Lenka
)
From the output we can see the names and their indexes by which we can access them.
Traditionally, arrays have been initialized with the array
function. In its simplest form, the function takes an arbitrary number of comma
separated values.
<?php
$names = array("Jane", "Lucy", "Timea", "Beky", "Lenka");
print_r($names);
Same array of female names is created with the array function.
Arrays can be initialized by assigning values to array indexes.
<?php $continents[0] = "America"; $continents[1] = "Africa"; $continents[2] = "Europe"; $continents[3] = "Asia"; $continents[4] = "Antarctica"; $continents[5] = "Australia"; print_r($continents);
We create the $continents array by assigning values to array
indexes. "America" has index 0, "Europe" has index 2 etc.
<?php
$continents = [ 1 => "America", 2 => "Africa",
3 => "Europe", 4 => "Asia", 5 => "Antarctica",
6 => "Australia" ];
print_r($continents);
In this example, we create the $continents array with
the indexes specified. By default, the first index is zero. In
our case, we start with 1.
$ php init4.php
Array
(
[1] => America
[2] => Africa
[3] => Europe
[4] => Asia
[5] => Antarctica
[6] => Australia
)
Now we have an array of continents with indexes that we have chosen.
The indexes do not have to be consecutive numbers.
<?php $languages[10] = "PHP"; $languages[20] = "Python"; $languages[30] = "Ruby"; $languages[40] = "PERL"; $languages[50] = "Java"; print_r($languages);
In the example, we have chosen numbers 10, 20, 30, 40, and 50 to be the indexes
for the $languages array.
When we do assignment initialization of a PHP array, we can omit the indexes. PHP automatically creates the indexes for us.
<?php $actors[] = "Philip Seymour Hoffman"; $actors[] = "Tom Cruise"; $actors[] = "Bill Paxton"; $actors[] = "Adrien Brody"; $actors[] = "Daniel Craig"; print_r($actors);
An array of actors is created. No specific indexes are set.
$ php init6.php
Array
(
[0] => Philip Seymour Hoffman
[1] => Tom Cruise
[2] => Bill Paxton
[3] => Adrien Brody
[4] => Daniel Craig
)
The PHP interpreter has created consecutive indexes starting from zero.
<?php $novels[10] = "Doctor Zhivago"; $novels[11] = "War and Peace"; $novels[] = "In Cold Blood"; $novels[20] = "Crime and Punishment"; $novels[] = "Catch XII"; print_r($novels);
In this script, we have omitted two indexes. The PHP will add them. It will create index 12 and index 21.
$ php init5.php
Array
(
[10] => Doctor Zhivago
[11] => War and Peace
[12] => In Cold Blood
[20] => Crime and Punishment
[21] => Catch XII
)
PHP has automatically created indexes 12 and 21.
The keys of an array can be strings too.
<?php
$countries = [
"de" => "Germany", "sk" => "Slovakia",
"us" => "United States", "ru" => "Russia",
"hu" => "Hungaria", "pl" => "Poland" ];
echo $countries["de"] . "\n";
echo $countries["sk"] . "\n";
We create a $countries array with string indexes.
$ php init8.php Germany Slovakia
PHP array element types
A PHP array can contain elements of various types.
<?php
$vals = ['sky', true, -4, [1, 2, 3, 4]];
foreach ($vals as $val) {
$t = gettype($val);
$res = match($t) {
'string' => 'value is a string',
'integer' => 'value is an integer',
'boolean' => 'value is a boolean',
'array' => 'value is an array',
default => 'unknown type'
};
echo "$res\n";
}
In the example, we have an array with elements of different types. With the
match expression and the gettype function, we get the type of each
element.
$ php types.php value is a string value is a boolean value is an integer value is an array
PHP perusing arrays
Next we read the contents of the arrays. There are several ways how we can display data from an array.
<?php $languages[10] = "PHP"; $languages[20] = "Python"; $languages[30] = "Ruby"; $languages[40] = "PERL"; $languages[50] = "Java"; echo $languages[10], "\n"; echo $languages[20], "\n"; echo $languages[30], "\n"; echo $languages[40], "\n"; echo $languages[50], "\n";
We can access data from an array by their index.
$ php peruse1.php PHP Python Ruby PERL Java
We have printed all five languages to the console.
<?php
$continents = [ "America", "Africa", "Europe",
"Asia", "Australia", "Antarctica" ];
$len = count($continents);
for ($i = 0; $i < $len; $i++) {
echo $continents[$i], "\n";
}
In this example, we use the for statement to peruse a
$continents array.
$len = count($continents);
First, we count the number of elements in the array with the count
function.
for ($i = 0; $i < $len; $i++) {
echo $continents[$i], "\n";
}
The for loop prints elements from the
array by indexes 0..$len-1.
<?php
$continents = [ "America", "Africa", "Europe", "Asia",
"Australia", "Antarctica" ];
foreach ($continents as $continent) {
echo $continent, "\n";
}
The easiest way to peruse an array is to use the foreach
statement. The statement goes through the array one by one and puts a current
element to the temporary $continent variable. It accesses data
without using their index or key.
<?php
$countries = [ "de" => "Germany", "sk" => "Slovakia",
"us" => "United States", "ru" => "Russia",
"hu" => "Hungaria", "pl" => "Poland" ];
function show_values($value, $key) {
echo "The $key stands for the $value\n";
}
array_walk($countries, 'show_values');
In the last example, we use the array_walk function to
peruse an array. It applies a user function to every member of an array.
The user function takes the key and the value of the item as parameters.
$ php walk.php The de stands for the Germany The sk stands for the Slovakia The us stands for the United States The ru stands for the Russia The hu stands for the Hungary The pl stands for the Poland
We print both the key and the value to the console in the sentence.
PHP array sort
First we are going to sort an arrays.
<?php
$names = [ "Jane", "Rebecca", "Lucy", "Lenka", "Ada" ];
echo "Unsorted: \n";
foreach ($names as $name) {
echo "$name ";
}
echo "\n";
sort($names);
echo "Sorted: \n";
foreach ($names as $name) {
echo "$name ";
}
echo "\n";
In the above script, we have a $names array. We use the
sort function to sort the contents of the array.
$ php sort.php Unsorted: Jane Rebecca Lucy Lenka Ada Sorted: Ada Jane Lenka Lucy Rebecca
The output of the script shows unsorted and sorted female names.
The rsort function sorts an array in reverse order.
<?php
$numbers = [ 12, 3, 5, 1, 6, 7, 10, 0, 9, 8, 11];
sort($numbers);
echo "Ascending order: \n";
foreach ($numbers as $n) {
echo "$n ";
}
echo "\n";
rsort($numbers);
echo "Descending order: \n";
foreach ($numbers as $n) {
echo "$n ";
}
echo "\n";
There is an array of integers. It is sorted in ascending and descending order.
sort($numbers);
The sort function sorts the integers in ascending order.
rsort($numbers);
The rsort function sorts the integers in descending order.
$ php sort2.php Ascending order: 0 1 3 5 6 7 8 9 10 11 12 Descending order: 12 11 10 9 8 7 6 5 3 1 0
In the following example, we show how to sort accented characters.
<?php
setlocale(LC_ALL, 'sk_SK.utf8');
$words = [ "ďateľ", "auto", "železo", "byt", "kocka", "dáma",
"zem", "autor", "ceduľa", "čižma"];
sort($words, SORT_LOCALE_STRING);
echo "Ascending order: \n";
foreach ($words as $w) {
echo "$w ";
}
echo "\n";
rsort($words, SORT_LOCALE_STRING);
echo "Descending order: \n";
foreach ($words as $w) {
echo "$w ";
}
echo "\n";
We have an array of Slovak words which contain specific accents.
setlocale(LC_ALL, 'sk_SK.utf8');
We set the Slovak locale using the setlocale function.
A locale represents a specific geographical, political, or cultural region.
$words = [ "ďateľ", "auto", "železo", "byt", "kocka", "dáma",
"zem", "autor", "ceduľa", "čižma"];
The $words is an array of accented Slovak words.
sort($words, SORT_LOCALE_STRING);
We sort the array in ascending order with the sort function. We
pass the SORT_LOCALE_STRING flag to the function, which tells
sort to take the locale into account.
$ php locale_sort.php Ascending order: auto autor byt ceduľa čižma dáma ďateľ kocka zem železo Descending order: železo zem kocka ďateľ dáma čižma ceduľa byt autor auto
The words are correctly sorted according to the Slovak standards.
Sometimes we need to perform custom sorting. For custom sorting,
we have the usort function in PHP.
<?php
$names = [ "Michael Brown", "Albert Einstein", "Gerry Miller",
"Tom Willis", "Michael Gray", "Luke Smith" ];
function sort_second_names($a, $b) {
$name1 = explode(" ", $a);
$name2 = explode(" ", $b);
return strcmp($name1[1], $name2[1]);
}
usort($names, 'sort_second_names');
foreach ($names as $name) {
echo "$name\n";
}
echo "\n";
We have an array of full names. The sort function would sort these
strings according to the first names, because they precede the second names. We
create a solution to sort these names according to their second names.
function sort_second_names($a, $b) {
$name1 = explode(" ", $a);
$name2 = explode(" ", $b);
return strcmp($name1[1], $name2[1]);
}
We have a custom sorting function. The names are split by the
explode function and the second names are compared with the
strcmp function.
usort($names, 'sort_second_names');
The usort function accepts the comparing function as its second
parameter.
$ php custom_sorting.php Michael Brown Albert Einstein Michael Gray Gerry Miller Luke Smith Tom Willis
The names are correctly sorted according to their second names.
PHP counting values in arrays
The count function counts the number of elements in the array. The
array_sum function calculates the sum of all values. The
array_product function calculates the product of values in the
array.
<?php $numbers = [ 1, 2, 4, 5, 2, 3, 5, 2 ]; $len = count($numbers); $sum = array_sum($numbers); $prod = array_product($numbers); echo "In the array, there are $len numbers\n"; echo "The sum of the numbers is $sum\n"; echo "The product of the numbers is $prod\n";
In the example, we have an array of numbers. We apply the above defined functions on the array.
$ php counting.php In the array, there are 8 numbers The sum of the numbers is 24 The product of the numbers is 2400
PHP unique values
In the following example, we find out unique values in an array.
<?php $numbers = array(3, 4, 4, 3, 2, 4); $count_values = array_count_values($numbers); print_r($count_values); $unique = array_unique($numbers); print_r($unique);
In this script, we have duplicates in the array. The
array_count_values function returns an array with the number of
occurrences for each value. The array_unique function returns an
array without duplicates.
$ php unique.php
Array
(
[3] => 2
[4] => 3
[2] => 1
)
Array
(
[0] => 3
[1] => 4
[4] => 2
)
The first array says that 3 is present twice, 4 three times, and 2 once. The
second array says that there are three values present in the array: 3, 4, and 2.
Value 3 has index 0, 4 has index 1 and 2 has index 4. The
array_unique function keeps the indexes untouched.
PHP slicing arrays
The array_slice function returns a sequence of elements from an
array as specified by its offset and length parameters.
<?php
$nums = range(1, 20);
$slice1 = array_slice($nums, 0, 3);
echo "Slice1:\n";
foreach ($slice1 as $s) {
echo "$s ";
}
echo "\n";
$slice2 = array_slice($nums, -3);
echo "Slice2:\n";
foreach ($slice2 as $s) {
echo "$s ";
}
echo "\n";
In the example, we create two slices of an array of integers.
$slice1 = array_slice($nums, 0, 3);
We create a slice starting from the first element; the length of the slice is three elements.
$slice2 = array_slice($nums, -3);
By giving a negative offset, the slice is created from the end of the array.
$ php slicing.php Slice1: 1 2 3 Slice2: 18 19 20
PHP array pointer
PHP has an internal array pointer. In the following example, we present functions that manipulate this pointer.
<?php
$continents = [ "America", "Africa", "Europe", "Asia", "Australia",
"Antarctica" ];
$item1 = current($continents);
$item2 = next($continents);
$item3 = next($continents);
$item4 = end($continents);
$item5 = prev($continents);
echo "$item1, $item2, $item3, $item4, $item5\n";
reset($continents);
while(list($idx, $val) = each($continents)) {
echo "Index: $idx, Value: $val\n";
}
In this example, we traverse the array using the functions that move the internal array pointer.
$item1 = current($continents); $item2 = next($continents); $item3 = next($continents); $item4 = end($continents); $item5 = prev($continents);
The current function returns the current element in the array. At
the beginning, it is the first element of the array. The next
function advances the pointer by one position. The end function
returns the last element. The prev element returns the element, one
position before the current one. In our case it is the next to the last element.
reset($continents);
while(list($idx, $val) = each($continents)) {
echo "Index: $idx, Value: $val\n";
}
Here we use the reset function to set the internal pointer to the
first element again and peruse the $continents array one more time.
$ php array_pointer.php America, Africa, Europe, Antarctica, Australia Index: 0, Value: America Index: 1, Value: Africa Index: 2, Value: Europe Index: 3, Value: Asia Index: 4, Value: Australia Index: 5, Value: Antarctica
PHP merging arrays
The array_merge function merges arrays.
<?php
$names1 = [ "Jane", "Lucy", "Rebecca" ];
$names2 = [ "Lenka", "Timea", "Victoria" ];
$names = array_merge($names1, $names2);
foreach ($names as $name) {
echo "$name ";
}
echo "\n";
In this example, we have two arrays: $names1 and $names2.
We use the array_merge function to create $names array by
merging the previous two arrays.
$ php merge.php Jane Lucy Rebecca Lenka Timea Victoria
The new array has six names.
PHP modifying arrays
It is possible to modify PHP arrays with array_push,
array_pop, array_shift, or array_unshift
functions.
<?php
$numbers = [ 1, 2, 3, 4 ];
array_push($numbers, 5, 6);
foreach ($numbers as $num) {
echo $num, " ";
}
echo "\n";
array_pop($numbers);
foreach ($numbers as $num) {
echo $num, " ";
}
echo "\n";
array_unshift($numbers, -1, 0);
foreach ($numbers as $num) {
echo $num, " ";
}
echo "\n";
array_shift($numbers);
foreach ($numbers as $num) {
echo $num, " ";
}
echo "\n";
In the above script, we use functions that modify the contents of an array.
We have a $numbers array that has 4 numbers: 1, 2, 3, and 4.
array_push($numbers, 5, 6);
The array_push function inserts one or more items to the end
of the array. Our array now contains values 1, 2, 3, 4, 5, and 6.
array_pop($numbers);
The array_pop function removes the last item from the array.
Our array stores now numbers 1, 2, 3, 4, and 5.
array_unshift($numbers, -1, 0);
The array_unshift function adds -1 and 0 to the beginning
of the array. The array contains values -1, 0, 1, 2, 3, 4, and 5.
array_shift($numbers);
Finally, the array_shift function removes the first item
from the array. Now we have values 0, 1, 2, 3, 4, and 5 in the array.
$ php modify.php 1 2 3 4 5 6 1 2 3 4 5 -1 0 1 2 3 4 5 0 1 2 3 4 5
PHP range function
The range function simplifies array creation by automatically
creating a sequence of elements. It accepts three parameters: start of sequence,
end of sequence, and an optional increment, which defaults to 1.
<?php
$numbers1 = range(1, 15);
foreach ($numbers1 as $num) {
echo "$num ";
}
echo "\n";
$numbers2 = range(15, 1, -1);
foreach ($numbers2 as $num) {
echo "$num ";
}
echo "\n";
The range function enables us to create a list of consecutive
numbers easily.
$numbers1 = range(1, 15);
An array with numbers 1, 2, ... 15 is created.
$numbers2 = range(15, 1, -1);
It is possible to create a descending sequence of values by specifying a negative increment.
$ php range.php 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
PHP randomizing array values
The array_rand function picks one or more random entries from an
array. The shuffle function randomizes the order of the elements in
an array.
<?php
$nums = range(1, 20);
echo ($nums[array_rand($nums)]) . "\n";
$r = array_rand($nums, 2);
echo $nums[$r[0]] . "\n";
echo $nums[$r[1]] . "\n";
shuffle($nums);
foreach ($nums as $n) {
echo "$n ";
}
echo "\n";
In the example, we pick random values from the array and randomize its order of elements.
echo ($nums[array_rand($nums)]) . "\n";
The array_rand function returns a random key from the
$num array.
$r = array_rand($nums, 2);
In this case, the array_rand function returns an array of two
random keys.
$ php randomize.php 4 2 19 13 19 4 3 17 11 20 16 10 9 8 14 15 12 18 2 6 5 1 7
This is a sample output of the randomize.php program.
PHP in_array function
The in_array function checks if a specific element
is inside an array.
<?php
$names = [ "Jane", "Adriana", "Lucy", "Rebecca" ];
if (in_array("Jane", $names)) {
echo "Jane is in the array\n";
} else {
echo "Jane is not in the array\n";
}
if (in_array("Monica", $names)) {
echo "Monica is in the array\n";
} else {
echo "Monica is not in the array\n";
}
Our script checks if 'Jane' and 'Monica' is in the $names array.
$ php inarray.php Jane is in the array Monica is not in the array
'Jane is in the array, but 'Monica' is not.
PHP array keys and values
PHP array is an associative array which consists of key and value pairs.
<?php
$domains = [ "sk" => "Slovakia", "de" => "Germany",
"hu" => "Hungary", "ru" => "Russia" ];
$keys = array_keys($domains);
$values = array_values($domains);
foreach ($keys as $key) {
echo "$key ";
}
echo "\n";
foreach ($values as $value) {
echo "$value ";
}
echo "\n";
The array_keys function returns all the keys of an array. The
array_values function returns all the values of an array.
$ php keysvalues.php sk de hu ru Slovakia Germany Hungary Russia
The first line consists of top level domain names. These were the keys of the
$domains array. The second line are the names of the corresponding
countries. These were the values of the array.
PHP array_walk function
The array_walk function applies a user defined function to
every member of the array.
<?php
$countries = [ "de" => "Germany", "sk" => "Slovakia",
"us" => "United States", "ru" => "Russia",
"hu" => "Hungaria", "pl" => "Poland" ];
function show_values($value, $key) {
echo "The $key stands for the $value\n";
}
array_walk($countries, 'show_values');
We have a $countries array. We apply the
show_values function to each element of the array. The function
simply prints the key and the value for each element.
$ php array_walk.php The de stands for the Germany The sk stands for the Slovakia The us stands for the United States The ru stands for the Russia The hu stands for the Hungaria The pl stands for the Poland
In this article we have covered PHP arrays.
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