How to sort a 2D array using PHP

In PHP, sorting a two-dimensional array is a very common task. When dealing with large amounts of data, sorting an array can greatly improve the efficiency of your code. For a single array, you can sort in ascending and descending order using functions like sort() and rsort(). However, for two-dimensional arrays, more code is required to implement sorting. This article will introduce how to use PHP to sort a two-dimensional array, including sorting by specified columns, multi-column sorting and custom sorting functions.

1. Sort by specified columns

We can use PHP’s built-in function usort() to achieve sorting. The usort() function is similar to the sort() function, but it allows us to use a custom function for sorting. To sort a 2D array by a specified column, we need to write a custom sort function and pass it to the usort() function. Here is a simple example, sorting by the second column in a two-dimensional array:

<?php 

function sortBySecondColumn($a, $b) {

    return $a[1] - $b[1];

}

$people = array(

    array(&#39;Tom&#39;, 23),

    array(&#39;Jack&#39;, 31),

    array(&#39;Mary&#39;, 27),

);

usort($people, &#39;sortBySecondColumn&#39;);

print_r($people);

?>

The output is:

Array

(

    [0] => Array

        (

            [0] => Tom

            [1] => 23

        )

    [1] => Array

        (

            [0] => Mary

            [1] => 27

        )

    [2] => Array

        (

            [0] => Jack

            [1] => 31

        )

)

Our custom function sortBySecondColumn() compares the array $a and the second column of $b and sort them based on its ascending or descending order. The usort() function will reorder the array according to our custom sorting function.

2. Multi-column sorting

If we need to sort by multiple columns, we can slightly change our custom function and add more conditions for each column. To sort the array by first and second column, please refer to the following code:

<?php 

function sortByMultipleColumns($arr, $col1, $col2) {

    foreach ($arr as $key => $row) {

        $column1[$key] = $row[$col1];

        $column2[$key] = $row[$col2];

    }

    array_multisort($column1, SORT_ASC, $column2, SORT_DESC, $arr);

    return $arr;

}

$people = array(

    array('Tom', 31),

    array('Tom', 25),

    array('Mary', 27),

    array('Mary', 29),

);

$people = sortByMultipleColumns($people, 0, 1);

print_r($people);

?>

The output will be:

Array

(

    [0] => Array

        (

            [0] => Mary

            [1] => 29

        )

    [1] => Array

        (

            [0] => Mary

            [1] => 27

        )

    [2] => Array

        (

            [0] => Tom

            [1] => 31

        )

    [3] => Array

        (

            [0] => Tom

            [1] => 25

        )

)

In the above code, for each column we have added an array and then use the array_multisort() function to sort the first column in ascending order and the second column in descending order. The final use returns the original array of sorted results.

3. Custom sorting function

When using a custom sorting function, we can define a sorting criterion for each element in the array. The custom function should return a value that is used to compare other elements in the array. This return value can be positive, negative, or zero, depending on how the elements are compared. Here is an example of a simple filter function:

<?php 

function sortByLength($a, $b) {

    return strlen($a) - strlen($b);

}

$cities = array("Berlin", "Athens", "Madrid", "Rome", "Paris");

usort($cities, &#39;sortByLength&#39;);

print_r($cities);

?>

The output is:

Array

(

    [0] => Rome

    [1] => Paris

    [2] => Berlin

    [3] => Athens

    [4] => Madrid

)

In the above example, we have defined a custom function sortByLength() that compares each The length of the array elements, sorts them in ascending order, and returns a positive, negative, or zero number.

Conclusion

In PHP, we sort a two-dimensional array by using the usort() function. Sorting by a specified column simply requires us to write a custom sort function and pass it to the usort() function. We can also sort by multiple columns by adding multiple conditions. Custom sort functions allow us to define more sorting criteria in the array. Every programmer should be familiar with these techniques when manipulating two-dimensional arrays.

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