Remove first and last instance of a string?

Question

How can I remove the first instance of a certain piece of html from a string.

I'm looking to remove

      </tr>
    </table></td>

  </tr

which is near the begining, but it also appears throughout the string.

I also need a way to do the same thing but the last instance of it.

Anyone know?

Answer 1

You'll be wanting str_replace. Replace that section with empty space (eg:"")

Answer 2

if you know roughly how close to the end of the string the substring that you want to replace is, you use substr_replace() with a negative $start and $length parameters, or you could just code up a function by hand to actually go through, find the last occurrence, then delete it. something like this (untested, written very quickly):

function replace_last_occurrence($haystack, $needle) {
    $pos = 0;
    $last = 0;

    while($pos !== false) {
        $pos = strpos($haystack, $needle, $pos);
        $last = $pos;
    }

    substr_replace($haystack, "", $last, strlen($needle));
}

similar, for first occurrence

function replace_first_occurrence($haystack, $needle) {        
    substr_replace($haystack, "", strpos($haystack, $needle, $pos), 
        strlen($needle));
}

you could also generalize this to replace the nth occurrence:

function replace_nth_occurrence($haystack, $needle, $n) {
    $pos = 0;
    $last = 0;

    for($i = 0 ; $i <= $n ; $i++) {
        $pos = strpos($haystack, $needle, $pos);
        $last = $pos;
    }

    substr_replace($haystack, "", $last, strlen($needle));
}

Answer 3

simplest way is to explode/split the string shift the top and pop the last then implode what's left with you're separator and concatenate the three.. i.e.:

$separator = 'your specified html separator here';
$bits = explode($separator , $yourhtml );
$start = array_shift($bits);
$end = array_pop($bits);
$sorted = $start . implode($separator,$bits) . $end;

(not tested)

Answer 4

This will delete last occurrence:

$needle = <<<EON
    </tr>
  </table></td>

</tr
EON;

if(preg_match('`.*('.preg_quote($needle).')`s', $haystack, $m, PREG_OFFSET_CAPTURE)) {
  $haystack = substr_replace($haystack, '', $m[1][1], strlen($m[1][0]));
}

As additional bonus you may ignore varying number of whitespaces within searched fragment like this:

if(preg_match('`.*('.implode('\s+', array_map('preg_quote', preg_split('`\s+`', $needle))).')`s', $haystack, $m, PREG_OFFSET_CAPTURE)) {
  $haystack = substr_replace($haystack, '', $m[1][1], strlen($m[1][0]));
}

Or even search case-insensitively by adding i-flag to regexp:

if(preg_match('`.*('.implode('\s+', array_map('preg_quote', preg_split('`\s+`', $needle))).')`is', $haystack, $m, PREG_OFFSET_CAPTURE)) {
  $haystack = substr_replace($haystack, '', $m[1][1], strlen($m[1][0]));
}