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 $tbl = []; echo ("\n"); foreach ($tbl as $row){[1,2,3,4], [10, 20, 30, 40], [100, 200, 300, 400]} ?>foreach ($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 $tbl = []; echo ("\n"); foreach ($tbl as $rk=>$rv){"row1" => ["key11" => "val11", "key12" => "val12", "key13" => "val13"], "row2" => ["key21" => "val21", "key22" => "val22", "key23" => "val23"], "row3" => ["key31" => "val31", "key32" => "val32", "key33" => "val33"]} ?>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 $arr3D = []; foreach ($arr3D as $arr) {[[1, 0, 9],[0, 5, 6],[1, 0, 3]], [[0, 4, 6],[0, 0, 1],[1, 2, 7]],} ?>foreach ($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.
functionshowarray($arr){foreach($arras$k=>$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 $arr3D = []; function showarray($arr){[[1, 0, 9],[0, 5, 6],[1, 0, 3]], [[0, 4, 6],[0, 0, 1],[1, 2, 7]],} showarray($arr3D); ?>foreach ($arr as $k=>$v){ if (is_array($v)){ showarray($v); } else { echo "$k => $v "; } } echo "\n";
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 $tbl = []; function showarray($arr){"row1" => ["key11" => "val11", "key12" => "val12", "key13" => "val13"], "row2" => ["key21" => "val21", "key22" => "val22", "key23" => "val23"], "row3" => ["key31" => "val31", "key32" => "val32", "key33" => "val33"]} showarray($tbl); ?>foreach ($arr as $k=>$v){ if (is_array($v)){ showarray($v); } else { echo "$k => $v "; } } echo "\n";
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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