dongyu8664 2016-08-16 02:41
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使用正则表达式PHP提取子字符串

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

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  • dsfovbm931034814 2016-08-16 02:56
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    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.

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