PHP - Multidimensional Array

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A multidimensional array is an array of arrays. In a PHP array, each element can be another array. If the array consists of values or key-value pairs with values being of singular scalar types, it is a one-dimensional array. If each element in an array is an array of one or more scalar values, it is a two-dimensional array.

A PHP array may be a two-dimensional associative array also, where each element of the outer array is key-value pair, the value being another associative array.

Syntax

Here is the Syntax for one dimensional indexed array −

 # one dimensional indexed array $arr = [10, 20, 30, 40];

Following is the Syntax for one dimensional associative array −

 # one dimensional associative array $arr = ["key1"=> "val1", "key2" => "val2", "key3" => "val3"];

Here is the Syntax for two dimensional indexed array −

 # two dimensional indexed array $arr = [ [1,2,3,4], [10, 20, 30, 40], [100, 200, 300, 400] ];

Below is the Syntax for two dimensional associative array −

 # two dimensional associative array $arr = [ "row1" => ["key11" => "val11", "key12" => "val12", "key13" => "val13"], "row2" => ["key21" => "val21", "key22" => "val22", "key23" => "val23"], "row3" => ["key31" => "val31", "key32" => "val32", "key33" => "val33"] ];

Iterating over a 2D Array

Two nested loops will be needed to traverse all the elements in a 2D array. The foreach loop is more suitable for array traversal. A 2D array is like a tabular representation of data in rows and columns.

Traversing Indexed 2D Array

The following example shows how you can reproduce a 2D array in a tabular form −

 <?php $tbl = [ [1,2,3,4], [10, 20, 30, 40], [100, 200, 300, 400] ]; echo ("\n"); foreach ($tbl as $row){ foreach ($row as $elem){ $val = sprintf("%5d", $elem); echo $val; } echo "\n"; } ?>

Output

It will produce the following output −

 1 2 3 4 10 20 30 40 100 200 300 400

Traversing Associative 2D Array

We can also employ two nested foreach loops to traverse a 2D associative array. Unpack each row of the outer array in row-key and row-value variables and traverse each row elements with the inner foreach loop.

 <?php $tbl = [ "row1" => ["key11" => "val11", "key12" => "val12", "key13" => "val13"], "row2" => ["key21" => "val21", "key22" => "val22", "key23" => "val23"], "row3" => ["key31" => "val31", "key32" => "val32", "key33" => "val33"] ]; echo ("\n"); foreach ($tbl as $rk=>$rv){ echo "$rk\n"; foreach ($rv as $k=>$v){ echo "$k => $v "; } echo "\n"; } ?>

Output

It will produce the following output −

 row1 key11 => val11 key12 => val12 key13 => val13 row2 key21 => val21 key22 => val22 key23 => val23 row3 key31 => val31 key32 => val32 key33 => val33

Accessing the Elements in a 2D Array

The $arr[$key] syntax of accessing and modifying an element in the array can be extended to a 2D array too. For a 2D indexed array, the jth element in the ith row can be fetched and assigned by using the expression "$arr[$i][$j]".

Indexed 2D Array

 <?php $tbl = [[1,2,3,4], [10, 20, 30, 40], [100, 200, 300, 400]]; # prints number in index 2 of the row 2 print ("Value at [2], [2] :" . $tbl[2][2]); ?>

Output

It will produce the following output −

 Value at [2], [2] :300

Similarly, the value at ith row and jth column may be set to another value.

 $tbl[2][2] = 250;

Associative 2D Array

If it is a 2D associative array, we need to use the row key and key-value variables of the desired column to access or modify its value.

 <?php $tbl = [ "row1" => ["key11" => "val11", "key12" => "val12", "key13" => "val13"], "row2" => ["key21" => "val21", "key22" => "val22", "key23" => "val23"], "row3" => ["key31" => "val31", "key32" => "val32", "key33" => "val33"] ]; print "value at row2 - key22 is " . $tbl["row2"]["key22"]; ?>

Output

It will produce the following output −

 value at row2 - key22 is val22

Multi-dimensional Array

In the above example, we had an array in which the associated value of each key was another collection of key-value pairs, and we call it as a 2D array. The concept can be extended to any number of levels. For example, if each element in the inner array associates its key to another array, it becomes a three-dimensional array.

Declaring a 3D Array

Here is an example of a three-dimensional array −

 $arr3D = [ [ [1, 0, 9], [0, 5, 6], [1, 0, 3] ], [ [0, 4, 6], [0, 0, 1], [1, 2, 7] ], ];

Traversing a 3D Array

To traverse such a 3D array, we need three nested foreach loops, as shown below −

 <?php $arr3D = [ [[1, 0, 9],[0, 5, 6],[1, 0, 3]], [[0, 4, 6],[0, 0, 1],[1, 2, 7]], ]; foreach ($arr3D as $arr) { foreach ($arr as $row) { foreach ($row as $element) { echo "$element "; } echo "\n"; } echo "\n"; } ?>

Output

It will produce the following output −

 1 0 9 0 5 6 1 0 3 0 4 6 0 0 1 1 2 7

However, it is entirely possible to declare an array extending upto any number of dimensions. For that we need to have a generalized solution to traverse an array of any dimensions.

Recurve Traversal of Multidimensional Array

The following code shows a recursive function that calls itself if the value of a certain key is another array. If we pass any array as an argument to this function, it will be traversed, showing all the k-v pairs in it.

 function showarray($arr) { foreach ($arr as $k=>$v) { if (is_array($v)) { showarray($v); } else { echo "$k => $v "; } } echo "\n"; }

Example

Let us pass the above 3D array $arr3D to it and see the result −

 <?php $arr3D = [ [[1, 0, 9],[0, 5, 6],[1, 0, 3]], [[0, 4, 6],[0, 0, 1],[1, 2, 7]], ]; function showarray($arr){ foreach ($arr as $k=>$v){ if (is_array($v)){ showarray($v); } else { echo "$k => $v "; } } echo "\n"; } showarray($arr3D); ?>

Output

It will produce the following output −

 0 => 1 1 => 0 2 => 9 0 => 0 1 => 5 2 => 6 0 => 1 1 => 0 2 => 3 0 => 0 1 => 4 2 => 6 0 => 0 1 => 0 2 => 1 0 => 1 1 => 2 2 => 7

This recursive function can be used with any type of array, whether indexed or associative, and of any dimension.

Example

Let us use a 2D associative array as argument to showarray() function −

 <?php $tbl = [ "row1" => ["key11" => "val11", "key12" => "val12", "key13" => "val13"], "row2" => ["key21" => "val21", "key22" => "val22", "key23" => "val23"], "row3" => ["key31" => "val31", "key32" => "val32", "key33" => "val33"] ]; function showarray($arr){ foreach ($arr as $k=>$v){ if (is_array($v)){ showarray($v); } else { echo "$k => $v "; } } echo "\n"; } showarray($tbl); ?>

Output

It will produce the following output −

 key11 => val11 key12 => val12 key13 => val13 key21 => val21 key22 => val22 key23 => val23 key31 => val31 key32 => val32 key33 => val33
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