Find the position of the first occurrence of any number in string

Question

Can someone help me with algorithm for finding the position of the first occurrence of any number in a string?

The code I found on the web does not work:

function my_offset($text){
    preg_match('/^[^\-]*-\D*/', $text, $m);
    return strlen($m[0]);
}
echo my_offset('[HorribleSubs] Bleach - 311 [720p].mkv');

Terreverte

try preg_match('/[\d]+/', $text, $m); – Broderic

Also, I find it handy to use an online "python regex repl" to test out and debug regex expressions. For example: pythex.org – Isadora

Answer 1

function my_ofset($text){
    preg_match('/^\D*(?=\d)/', $text, $m);
    return isset($m[0]) ? strlen($m[0]) : false;
}

should work for this. The original code required a - to come before the first number, perhaps that was the problem?

Vicinal

if there is no number in string it returns length of original string? – Terreverte

@gašper: Right. Can be fixed, but Stanislav's solution is much better. – Vicinal

Why is his solution better? if there is no number in string it returns me 1 (with his algorithm). if i use yours it returns me something logical (string length). – Terreverte

@gašper I've edited mine. If there's no number it now returns string length as well. I guess it's better because a) it searches exactly for numbers, not for non-numbers and b) it utilizes preg_match built-in feature which is always better than reinventing a bike. I hope Tim agrees with me :-) – Mechanical

@gašper: Well, my solution is kind of bent-over backwards (count the number of non-digits until the first digit). Also, thinking about it, I expect my solution to require an additional check whether there has been a match at all. I'm not a PHP programmer, so I'm building that code upon snippets created by RegexBuddy using my regex. – Vicinal

Answer 2

The built-in PHP function strcspn() will do the same as the function in Stanislav Shabalin's answer when used like so:

strcspn( $str , '0123456789' )

Examples:

echo strcspn( 'That will be $2.95 with a coupon.' , '0123456789' ); // 14
echo strcspn( '12 people said yes'                , '0123456789' ); // 0
echo strcspn( 'You are number one!'               , '0123456789' ); // 19

HTH

Sheaff

I bet that this is about 20 times faster than any regex solution – Binge

note: it works fine with non-latin text, but then don't use mb_substr – Depositary

Answer 3

function my_offset($text) {
    preg_match('/\d/', $text, $m, PREG_OFFSET_CAPTURE);
    if (sizeof($m))
        return $m[0][1]; // 24 in your example

    // return anything you need for the case when there's no numbers in the string
    return strlen($text);
}

Mechanical

Makes more sense. I (and RegexBuddy) didn't know about PREG_OFFSET_CAPTURE :) – Vicinal

Answer 4

I can do regular expressions but I have to go into an altered state to remember what it does after I've coded it.

Here is a simple PHP function you can use...

function findFirstNum($myString) {

    $slength = strlen($myString);

    for ($index = 0;  $index < $slength; $index++)
    {
        $char = substr($myString, $index, 1);

        if (is_numeric($char))
        {
            return $index;
        }
    }

    return 0;  //no numbers found
}

Pipkin

Answer 5

Problem

Find the first occurring number in a string

Solution

Here is a non regex solution in javascript

var findFirstNum = function(str) {
    let i = 0;
    let result = "";
    let value;
    while (i<str.length) {
      if(!isNaN(parseInt(str[i]))) {
        if (str[i-1] === "-") {
          result = "-";
        }
        while (!isNaN(parseInt(str[i])) && i<str.length) {
          result = result + str[i];
          i++;
        }
        break;
      }
      i++;
    }
    return parseInt(result);  
};

Example Input

findFirstNum("words and -987 555");

Output

-987

Afra