Extracting Sub-String using regex PHP

Question

I have a need to extract a sub-string from a longer string. I know how I would approach it using PHP posstr(); and strpos();, but the data is very large and I suspect that it would be more efficient if I could extract the part string using regex.

For example, if I have a number, (say a latitude) that has the format

"3203.79453"

where the the two characters before and "all" the characters after the decimal point represent decimal seconds, then to obtain the decimal latitude I need to compute the following:

32 + (03.79453)/60 = 32.06324217

So in essence I need a regex method of extracting the sub-string "03.79453".

So two questions how do I achieve it using regex and is it faster than using the method of using strpos() and posstr().

Thanks

scrowler · Accepted Answer · 2016-08-16 02:56:33Z

2

It's easy to achieve with both options:

substr($line, strpos($line, '.') - 2);

or:

preg_match("/(\d{2}\..*)/", $line, $matches);

As for performance, I guess you would need to benchmark it. I've done a quick test to compare the performance of each example by running one million reps of each of those lines:

preg_match: average around 1.6 seconds for 1,000,000 matches
substr: average around 0.85 seconds for 1,000,000 matches

In this case it seems clear that using substr is the winner in terms of performance.

answered Aug 16, 2016 at 2:56

scrowler

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1 Comment

user5212066 Over a year ago

Perfect. Thanks very much Robbie.

Poiz · Accepted Answer · 2016-08-16 02:58:53Z

1

You could use preg_replace() like so:

    <?php

        $geoCoordinate  = "3203.79453";
        $degrees        = preg_replace("#(\d{2}\.\d*?$)#", "",          $geoCoordinate);
        $seconds        = preg_replace("#(\d*?)(\d{2}\.\d*?)#", "$2",   $geoCoordinate);
        $degAndSecs     = round($degrees + ($seconds/60), 8);

        var_dump($degAndSecs);  //<== PRODUCES::: float 32.06324217

answered Aug 16, 2016 at 2:58

Poiz

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