Multi-Dimensional Arrays in PHP

Today we are going to learn the manipulation of multi-dimensional arrays in this Multi-Dimensional Arrays in PHP.

• Arrays are used to store more than one similar type values in a single variable.
• These values can be anything like strings, integers, floats, objects and even other arrays.
• When we include arrays in array, we deal with multi-dimensional arrays.
• There are situations when we need to store multiple values for an entity and group such entities at one place. I mean we can store the values such as name, quantity and price for different products. Multi-dimensional arrays are better storages in such situations.
• We can have any number of dimensions in multi-dimensional arrays.
• Two-dimensional and Three dimensional arrays are mostly used. We can even have four, five, and six up to n dimensional arrays.
• The dimensions of an array indicate the number of indices required to fetch a value from the array. Such as two dimensional arrays will require 2 dimensions and three dimensional arrays will require 3 dimensions.
• Multi-dimensional arrays can be indexed as well as associative arrays.
• Let us go through various examples of multi-dimensional arrays:

Two-dimensional arrays:

• • • A two dimensional array means array of arrays.
      • Example of indexed two dimensional array:

<?php
$marks=array(
   array(80,89,79),
   array(90,78,87),
   array(78,90,78)
);
?>

• • • Here, we have declared a $marks two-dimensional array since it has 3 arrays inside an array.
    • This is an indexed array because the arrays will be given indexes 0, 1 and 2 automatically.
    • And in turn the values inside the arrays will also be given indices starting from 0 each.
    • Since it is a 2-dimensional array, it requires 2 dimensions i.e. row and column to retrieve the values.
    • Let is demonstrate it by writing a code.
    • To demonstrate it create a new folder named multi_arrays in the htdocs folder in the xampp folder in C drive. Open a new notepad++ document and save it as index.php in this newly created multi_arrays folder
    • Write the following code in index.php file:

<?php

echo "Indexed 2-dimensional array:<br>";
$marks=array(
	array(80,89,79),
	array(90,78,87),
	array(78,90,78)
);

//displaying array elements manually
echo "<strong>marks array displayed manually:</strong><br>";
echo $marks[0][0]."  ".$marks[0][1]."  ".$marks[0][2]."<br>";
echo $marks[1][0]."  ".$marks[1][1]."  ".$marks[1][2]."<br>";
echo $marks[2][0]."  ".$marks[2][1]."  ".$marks[2][2]."<br><br>";

//displaying array elements at once using for loop.
echo "<b>marks array displayed using nested for loop:</b><br>";
for($r=0;$r<count($marks);$r++)
{
	for($c=0;$c<count($marks[$r]);$c++)
	{
		echo $marks[$r][$c]."   ";
	}
	echo "<br>";
}

• • • In the above code we have declared a $marks array containing marks of 3 students in 3 subjects each.
    • These elements can be accessed using 2 dimensions, one for row and other for column.
    • The 3 arrays in the $marks array are indexed with 0, 1 and 2. These will be considered as rows.
    • The elements inside each row are indexed starting with 0 (zero) each. These are considered as columns.
    • So the first element in first row can be accessed as $marks[0][0], second element in first row can be accessed as $marks[0][1] and so on.
    • The code for accessing all elements manually is given below:

echo "<strong>marks array displayed manually:</strong><br>";
echo $marks[0][0]."  ".$marks[0][1]."  ".$marks[0][2]."<br>";
echo $marks[1][0]."  ".$marks[1][1]."  ".$marks[1][2]."<br>";
echo $marks[2][0]."  ".$marks[2][1]."  ".$marks[2][2]."<br><br>";

• • • The elements are accessed according to their indexes in each row and column.
    • If there is a big 2-dimensional array containing large number of elements, it is not possible to access such a large number of elements manually.
    • Thus we can use a nested for loop for this purpose. Why nested only, because we have more than one indices in case of multi-dimensional arrays.
    • If there are 2 indices then 2 for loops, if there are 3 indices then 3 for loops and so on.
    • Let us see how to access array values using loops. The code is given below:

echo "<b>marks array displayed using nested for loop:</b><br>";
for($r=0;$r<count($marks);$r++)
{
	for($c=0;$c<count($marks[$r]);$c++)
	{
		echo $marks[$r][$c]."   ";
	}
	echo "<br>";
}

• • • Here, we have used the outer for loop for row and inner for loop for column.
    • The variable $r is the counter for row for loop and $c is the counter for column for loop.
    • $r is first initialized to 0 (zero) i.e. zeroth row.
    • The condition given is

      $r<count($marks)

      . Here, the function count() will count the number of arrays present in the array $marks and return that number. In our case this condition is equal to $r<3, because we have 3 arrays in $marks array.

    • In the inner for loop. $c is initialized to 0 (zero) i.e zeroth column.
    • The condition given here is

      $c<count($marks[$r])

      . Here, the parameter in count() function is $marks[$r], this indicates the particular row in the $marks array. All together it means that the count function will count the number of elements in the particular row given. For example if the value of $r is 0, it will count the number of elements in zeroth row and return that number. So if $r has value 0, the condition will be like $c<3. This is because the zeroth row contains 3 elements/columns.

    • So all the elements are displayed using echo function accessing the indices using $r and $c variables.
    • The statement is shown below:

echo $marks[$r][$c]."   ";

• • • A space is left after every element in a row.
    • After completion of one row a break statement is executed to leave a line break and start a new row on new line.
    • The output is shown below:

fig 1

• • • • Example of associative two dimensional array:
    • The same array in indexed form given above can be written in associative form as shown below:

$marks1=array(
	array("Maths"=>80,"Physics"=>89,"Chemistry"=>79),
	array("Maths"=>90,"Physics"=>78,"Chemistry"=>87),
	array("Maths"=>78,"Physics"=>90,"Chemistry"=>79)
);

• • • It is similar to indexed array, but only each value is given a key for it like Maths, Physics and Chemistry.
    • Let us access all the elements using for loop. But we have an associative array which is accessed using a foreach loop. So let us see the code given below which is written in index.php file:

echo "Associative 2-dimensional array:<br>";

$marks1=array(
	array("Maths"=>80,"Physics"=>89,"Chemistry"=>79),
	array("Maths"=>90,"Physics"=>78,"Chemistry"=>87),
	array("Maths"=>78,"Physics"=>90,"Chemistry"=>79)
);
echo "<ul>";
for($r=0;$r<count($marks1);$r++)
{
	echo "<li>";
	foreach($marks1[$r] as $key=>$value)
	{
		echo $key." = ".$value."  ";
	}
	echo "</li>";
	echo "<br><br>";
}
echo "</ul>";

• • • Here, the above associative 2-dimensional array values are displayed using a nesting of for loop and foreach loop.
    • The for loop is used to loop through the number of arrays present in the $marks1 array and foreach loop is used to loop through the key-value pairs.
    • Here we now know that the counter $r of for loop is initialized to 0 and loops till the condition doesn’t become false i.e. till all the rows are not traversed completely.
    • The foreach loop is used to go through each and every key-value pair.
    • It takes every row and selects each key-value pair in it as shown in the statement below:

foreach($marks1[$r] as $key=>$value)

• • • $marks1[$r] selects the particular row, as is the keyword and $key fetches the key and $value fetches the value of that key from that particular row using $key=>$value.
    • The values of $key and $value are then displayed using echo function.
    • Each row is printed on separate line and the HTML unordered list is used to display the data.
    • The output is shown below:

• • • fig 2

• • Three-dimensional arrays:
    • A three-dimensional array has arrays in an array and the inner arrays in turn have arrays inside it.
    • These 3-dimensional arrays require 3 indices to access the values stored inside it.
    • A three dimensional array is characterized by its height, width and depth.
    • Let us see an example of 3-dimensional array:

$product=array(
		    array(
			   array("Epson Printer L110",100,4500),
			   array("Canon Printer",100,5000),
			   array("HP Laptop",500,40000)
			),
			array(
				array("Micromax Canvas Lite",200,9000),
				array("Samsung Galaxy",300,15000),
				array("LAVA",100,4000)
			)
			array(
				array("Sandisk 16 GB Pendrive",500,500),
				array("Card Reader",500,50),
				array("UPS",200,3000)
			)

);

• • • Here, we have declared a $product three dimensional array since it has 2 arrays in an array and the 2 arrays inturn have 3 arrays each.
    • The array contains the product’s name, product quantity and product price.
    • This will require 3 loops to access its elements.
    • Let us demonstrate how to do it. The code is given below:

echo "3-dimensional array:<br>";

$product=array(
		    array(
			   array("Epson Printer L110",100,4500),
			   array("Canon Printer",100,5000),
			   array("HP Laptop",500,40000)
			),
			array(
				array("Micromax Canvas Lite",200,9000),
				array("Samsung Galaxy",300,15000),
				array("LAVA",100,4000)
			),
			array(
				array("Sandisk 16 GB Pendrive",500,500),
				array("Card Reader",500,50),
				array("UPS",200,3000)
			)
);

// accessing elements from 3-dimensional product array.
echo "<table border=1 cellpadding=5 cellspacing=5>";
echo "<tr>";
echo "<th>Product</th>";
echo "<th>Quantity</th>";
echo "<th>Price</th>";
echo "</tr>";

for($l=0;$l<3;$l++)
{
	echo "<tr>";
	for($r=0;$r<3;$r++)
	{
		
		for($c=0;$c<3;$c++)
		{
			echo "<td>".$product[$l][$r][$c]."</td>";
		}
		echo "</tr>";
		
	}
	
}
echo "</table>";

• • • In the above code we have used 3 for loops to display the $product array content.
    • The values are displayed in a HTML table.
    • The outer for loop is used for the layer. You imagine a three dimensional array as layers of 2-dimensional arrays one above the other. We consider this layer in the first for loop.
    • Next the second for loop is used for rows and the inner most for loop is used for columns.
    • The value is displayed using echo function as shown below:

echo "<td>".$product[$l][$r][$c]."</td>";

• • • The output of the above code is shown below:

fig 3

• • In the similar way arrays with multiple dimensions like four, five etc. can also be used. But mostly in the applications multi-dimensional arrays with 2 and 3 dimensions are enough.

Thus we finished learning how to make use of multi-dimensional arrays in this Multi-dimensional arrays in PHP.

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