Re: Verifying data in large number of textfiles

You might try using a diff utility, but on 5000 files that a lot of comparisons. However, most diff's do have options to allow you to ignore some whitepace and other "inconsequential" differences.

You could create an Digest::MD5 digest for each file and the compare those. If the files are identical, the md5s will be also. However, even small whitespace differences will change the outcomes, which may be too sensitive for your purpose.

I think I would try preprocessing the files to strip all the whitespace, and then produce an md5 from the results. That probably still doesn't guarentee that the files aren't the same data sets with just variations in formatting (eg. 10.0 -v- 10 -v- 1e1 etc), but it should reduce the possibilities.

Beyond that, a lot depends on the size, nature and format of the data and the reliability of your ripping process.

Examine what is said, not who speaks.

"Efficiency is intelligent laziness." -David Dunham
"Think for yourself!" - Abigail
"Memory, processor, disk in that order on the hardware side. Algorithm, algorithm, algorithm on the code side." - tachyon

Comment on Re: Verifying data in large number of textfiles

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Re^2: Verifying data in large number of textfiles by dchandler (Sexton) on Aug 18, 2004 at 01:36 UTC
is an md5 digest like a fingerprint for each file? that too might be useful...	[reply]
Re^3: Verifying data in large number of textfiles by BrowserUk (Patriarch) on Aug 18, 2004 at 03:04 UTC
Yes. A bit like a checksum, but being 128 bits, it's reasonably safe to assume that if the generated numbers are the same, the data from which they are generated is also. Note: Reasonably safe means "Not guarenteed", but for your application it's perfect as you only need to manually compare those files generating the same signature. If they are indeed the same, then you can discard one of them. (Incidently, you ever find two substantially different files that generate the same md5, it would be interesting to see them. :) The problem with this, as I mentioned, is that even inconsequential differences, like trailing whitespace, will get you different md5s. Hence the suggestion to strip the whitespace before generating the md5s. If the data contains numbers, you might want to "normalise" those to some consistant format (using sprintf for example). Likewise, if there is any chance that text may sometimes be identical except for case, you could normalise that to all lower or upper. In the end, you get 5000 (big) numbers. Stick them in a hash, checking for their previous existance first. Any duplicates and you have found what your looking for. Examine what is said, not who speaks. "Efficiency is intelligent laziness." -David Dunham "Think for yourself!" - Abigail "Memory, processor, disk in that order on the hardware side. Algorithm, algorithm, algorithm on the code side." - tachyon	[reply]