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gzip vs bzip2 at compressing random strings?

Terminal - gzip vs bzip2 at compressing random strings?
< /dev/urandom tr -dc A-Za-z0-9_ | head -c $((1024 * 1024)) | tee >(gzip -c > out.gz) >(bzip2 -c > out.bz) > /dev/null
2009-04-04 13:23:01
User: jnash
Functions: bzip2 gzip head tee tr
gzip vs bzip2 at compressing random strings?

Does that count as a win for bzip2?


There are 5 alternatives - vote for the best!

Terminal - Alternatives

Know a better way?

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What others think

I use bzip2 too all the time, even thought it's much slower, thinking it compresses way better. But what's that, like .01 % smaller? I think I'm reverting to gzip.

Comment by cbilson 357 weeks and 5 days ago

I use 'lzma --fast'. The speed is comparable to gzip and the compression is better than bzip2.

Comment by atoponce 357 weeks and 5 days ago

Love the one liner on its own merits, but disagree with the method. The data produced here isn't a fair representation. Such random data (though within a smaller gamut of 63 characters than the full 256) gives a result more akin to compressing an already compressed file.

Comment by peterc 357 weeks and 5 days ago

I don't know the case for binary files but for text files bzip2 is significantly better. When I ran the following to compress human genome DNA sequence (3,010 MB total size) by gzip and bzip2:

cat human_genome | tee >(gzip -c > out.gz) >(bzip2 -c > out.bz) > /dev/null

The sizes of output files are;

out.gz 892MB

out.bz 782MB

Comment by alperyilmaz 357 weeks and 5 days ago

@peterc: Of course. Thats why I titled it gzip vs bzip2 at compressing _random_ strings. This wasn't any technical comparison. I was just curious on what'd win on random strings :)

@atoponce: Ah. Then you might want to add it to the races like so.. >(lzma --fast ...)

Comment by jnash 357 weeks and 5 days ago

There are many types of random though. Random strings of normal distribution and format and really, really random strings. However, @alperyilmaz's experiment with DNA sequences is interesting. I guess DNA sequences aren't as random as I thought!

Just for fun, I wondered what the performance would be like on the first sort of "random", say Markov chain generated text:

./markov | head -c 10000 | tee >(gzip -c > out.gz) >(bzip2 -c > out.bz) > /dev/null

(markov generates several hundred Markov generated sentences using Macbeth as the source text)

I tried it three times. In each case, the bzip2 file was 90%, 91%, and 90% of the gz file. So not as amazing as I'd have expected (and worse than the DNA sequence!!)

Point of all of this? God knows but it was fun for a few minutes ;-)

Comment by peterc 357 weeks and 4 days ago

And for those people voting this down, I think it's worth voting up not for what it specifically does, but because the latter part of the line provides a nice technique for comparing two compression techniques nonetheless :)

Comment by peterc 357 weeks and 4 days ago

Your point of view

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