Generating an array

Generate and fill a new array: range()

To generate an array with a sequence of values, you can utilize the range() function.

For instance, if you need to create an array containing the values 1, 2, 3, 4, 5 (from 1 to 5), you can employ the range() function with two arguments. The first argument represents the lower value, and the second argument represents the higher value:

$a = range(1,5);
print_r($a);
/*
Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
)
*/

To create a similar array with descending values, you can set the higher value as the first argument. The range() function implementation automatically detects the descending approach if the first argument is greater than the second one:

$a = range(5,1);
print_r($a);
/*
Array
(
    [0] => 5
    [1] => 4
    [2] => 3
    [3] => 2
    [4] => 1
)
*/

If you use ASCII characters instead of integers, you will create an array with the sequence of characters:

$a = range('a','e');
print_r($a);
/*
Array
(
    [0] => a
    [1] => b
    [2] => c
    [3] => d
    [4] => e
)
*/

You can also create character arrays in descending order:

$a = range('e','a');
print_r($a);
/*
Array
(
    [0] => e
    [1] => d
    [2] => c
    [3] => b
    [4] => a
)
*/

If you are using strings instead of single characters, just the first character of the string will be considered:

$a = range('anaconda','elephant');
print_r($a);
/*
Array
(
    [0] => a
    [1] => b
    [2] => c
    [3] => d
    [4] => e
)
*/

If you intend to create an array containing 'A'..'Z' and 'a'..'z', you cannot directly use range('A', 'z'). This is because the range() function for characters is based on the ASCII table. In the middle of the ASCII table, between upper and lower case characters, there are additional characters such as [ \ ] ^ _.

Instead, you can use the range() function separately for upper case and lower case characters, and then merge the two sequences:

$a = array_merge(range('A','Z'), range('a','z'));

You can also generate a range of floating-point numbers. In this case, each number in the sequence is incremented by 1.0 from the previous value:

$a = range(1.5, 4.45);
print_r($a);
/*
Array
(
    [0] => 1.5
    [1] => 2.5
    [2] => 3.5
)
*/

Step

The third parameter (optional, with a default value of 1) determines the increment for each element. For example, if you want to generate odd numbers within the range of 1 to 10:

$a = range(1,10,2);
print_r($a);
/*
Array
(
    [0] => 1
    [1] => 3
    [2] => 5
    [3] => 7
    [4] => 9
)
*/

The step parameter can be negative. In such cases, a sequence in descending order is created:

$a = range(10,1,-2);
print_r($a);
/*
Array
(
    [0] => 10
    [1] => 8
    [2] => 6
    [3] => 4
    [4] => 2
)
*/

If you use a negative step value and the first parameter is lower than the second one, a ValueError exception is raised:

$a = range(1,10,-2);

Will raise the ValueError exception:

ValueError  range(): Argument #3 ($step) must be greater than 0 for increasing ranges.