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Some drops of PHP

Counting character occurrences in a string with PHP

Counting characters via count_chars()

The count_chars() function in PHP analyzes a given string and counts the occurrences of each character (including whitespace and special characters). The function’s behavior can be customized using the mode parameter, which determines the type of data returned, such as character counts, unique characters, or unused characters.

Syntax and parameters

count_chars(string $string, int $mode = 0): array|string

Parameters

  • string (required): The input string to be analyzed.
  • mode (optional): An integer that determines the return value format. The default is 0.
    • 0: Returns an array with the character code as key and its frequency as value.
    • 1: Same as 0, but includes only characters with a frequency > 0.
    • 2: Same as 0, but includes only characters with a frequency = 0.
    • 3: Returns a string containing all unique characters.
    • 4: Returns a string containing all unused characters.

With the default mode (0), the function returns a list of all characters and their frequencies, including characters with a frequency of 0.

Return value

The function returns an array or a string depending on the mode parameter.

Use cases

1. Character frequency analysis

$text = "Hi Folks! We love PHP! PHP is amazing!";
$charCount = count_chars($text, 1);


print_r($charCount);
/*
Array
(
    [32] => 7
    [33] => 3
    [70] => 1
    [72] => 3
    [80] => 4
    [87] => 1
    [97] => 2
    [101] => 2
    [103] => 1
    [105] => 3
    [107] => 1
    [108] => 2
    [109] => 1
    [110] => 1
    [111] => 2
    [115] => 2
    [118] => 1
    [122] => 1
)
*/


foreach ($charCount as $char => $count) {
    echo "'" . chr($char) . "' occurs $count time(s)\n";
}


/*
Character frequency in 'Hi Folks! We love PHP! PHP is amazing!':
' ' occurs 7 time(s)
'!' occurs 3 time(s)
'F' occurs 1 time(s)
'H' occurs 3 time(s)
'P' occurs 4 time(s)
'W' occurs 1 time(s)
'a' occurs 2 time(s)
'e' occurs 2 time(s)
'g' occurs 1 time(s)
'i' occurs 3 time(s)
'k' occurs 1 time(s)
'l' occurs 2 time(s)
'm' occurs 1 time(s)
'n' occurs 1 time(s)
'o' occurs 2 time(s)
's' occurs 2 time(s)
'v' occurs 1 time(s)
'z' occurs 1 time(s)
*/

This example demonstrates how to analyze the frequency of characters in a string, which can be useful for tasks like basic text analysis or simple encryption techniques.

2. Finding unique characters

$text = "Hi Folks! We love PHP! PHP is amazing!";
$uniqueChars = count_chars($text, 3);
echo "Unique characters: $uniqueChars" . PHP_EOL;
// Unique characters:  !FHPWaegiklmnosvz

This use case shows how to extract all unique characters from a string, which can be helpful in scenarios like generating character sets or validating input.

3. Checking for unused characters

$text = "Hi Folks! We love PHP! PHP is amazing!";
$unusedChars = count_chars($text, 4);
echo "Unused ASCII characters: " . bin2hex($unusedChars) . "\n";

This example illustrates how to find characters not used in a given string, which can be useful for tasks like checking if a string is a pangram or identifying available characters for encoding.

Common pitfalls

  1. Case sensitivity: count_chars() is case-sensitive. ‘A’ and ‘a’ are treated as different characters.

  2. Multibyte characters: this function only works with single-byte encoded strings. For multibyte encoded strings (e.g., UTF-8), use mb_split() in combination with array_count_values().

  3. Performance: this function might be memory-intensive for very large strings. Consider using alternative methods for large-scale text processing.

Additional resources