Question

Is there an efficient way to split a string containing a list of email addresses into groups of say 50? Say I have a string that contains emails in a comma-separated format. Something like… [e-mail],[e-mail],[e-mail] and so on.

The most obvious way to do this would probably be an array, but is there a way to do it with string functions? I have looked at substr and str_split and they don’t quite seem to do the job.

Answer 1

It should be by far more efficient to search for the 50th occurrence of a comma and split the string after this.
So find this Position. I think this http://www.php.net/manual/en/function.strpos.php#102336 should be a solution for that.
Then split the string with substr and remove the comma at pos 1 of the new string.

Shortened PHP-Code to fit your needs:

<?php 

function strnpos( $haystack, $needle, $nth, $offset = 0 ) { 
    //  If needle is not a string, it is converted to an integer and applied as the ordinal value of a character. 
    if(!is_string($needle)) 
        $needle = chr((int)$needle ); 

    //  Are the supplied values valid / reasonable? 
    $len = strlen( $needle ); 
    if(1 > $nth || 0 === $len) 
        return false; 

    //  $offset is incremented in the call to strpos, so make sure that the first 
    //  call starts at the right position by initially decreasing $offset by $len. 
    $offset -= $len; 
    do { 
        $offset = strpos( $haystack, $needle, $offset + $len ); 
    } while( --$nth  && false !== $offset ); 

    return $offset;
} 

$emails_str = '[e-mail],[e-mail],[e-mail],...';

$pos = strnpos($emails_str, ',', 50, 0);
while($pos) {
    // Do sth. with the group...
    echo substr($emails_str, 0, $pos), PHP_EOL; 

    // Cut this part out of the string
    $emails_str = substr($emails_str, $pos+1);
    $pos = strnpos($emails_str, ',', 50, 0);
}