Why are boolean and NULL not counted when using array_count_values?

array_count_values ​​is a very practical function in PHP that counts the number of occurrences of all values ​​in an array. This function returns an associative array where the keys of the array are the values ​​in the original array, and the values ​​of the array are the number of times these values ​​appear in the original array.

However, sometimes when using array_count_values , you may find that boolean values ​​( true and false ) and NULL do not appear in the statistics. Why is this? Let’s analyze it today.

1. Introduction to array_count_values ​​function

First, let’s review the basic usage of the array_count_values ​​function. This function takes an array as an argument and returns a new array, counting the number of occurrences of each element in the array. For example:

 $arr = ['apple', 'banana', 'apple', 'orange', 'banana', 'banana'];
$result = array_count_values($arr);
print_r($result);

The output will be:

 Array
(
    [apple] => 2
    [banana] => 3
    [orange] => 1
)

2. Reasons for Boolean and NULL to be ignored

Next, we analyze why Boolean and NULL are ignored.

Boolean value

In PHP, the boolean values ​​true and false are converted to integer values ​​1 and 0 , and in the array_count_values ​​function, the boolean values ​​are considered to be the same value. Specifically, true and false are treated as the same 1 and 0 , and array_count_values ​​merge them when processing arrays. Therefore, if there are multiple boolean values ​​in the array, their occurrences will be merged into the corresponding integer value instead of counting the boolean values ​​separately.

 $arr = [true, false, true, 1, 0];
$result = array_count_values($arr);
print_r($result);

The output will be:

 Array
(
    [1] => 3
    [0] => 2
)

You can see that true and 1 are merged into 1 , while false and 0 are merged into 0 , so the boolean value is not counted separately.

NULL

For NULL values, PHP also has a special behavior when processing arrays. When array_count_values ​​is used, NULL is ignored because it is usually considered "null" in PHP. If you need to count the number of occurrences of NULL , you can consider converting it to another value first, or processing it in other ways.

For example, consider the following code:

 $arr = [NULL, 'apple', NULL, 'banana', 'apple'];
$result = array_count_values($arr);
print_r($result);

The output will be:

 Array
(
    [apple] => 2
    [banana] => 1
)

As you can see, NULL does not appear in the result. To solve this problem, you can replace all NULL values ​​with a specific value, such as 'NULL' before calling array_count_values , and then perform statistics.

 $arr = [NULL, 'apple', NULL, 'banana', 'apple'];
$arr = array_map(function($value) {
    return $value === NULL ? 'NULL' : $value;
}, $arr);
$result = array_count_values($arr);
print_r($result);

The output will be:

 Array
(
    [NULL] => 2
    [apple] => 2
    [banana] => 1
)

This way, you can include NULL values ​​when stating.

3. Summary

array_count_values ​​is a very convenient function to count the number of occurrences of each value in an array. However, because Boolean and NULL values ​​in PHP have special conversion and ignorance behaviors when processing, they are not counted separately. If you need to deal with these special cases, you can manually replace these values ​​before calling array_count_values , or type conversion to ensure that they can be counted correctly.

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