A simple run length encoder built in Ruby for encoding bit vector strings and "compressing" files via this method. The run length encoder will reduce the length of a bit vector. If the file is more heavily composed of one value than another (0s or 1s), the encoding will compress fairly successfully. If not, it's a mediocre compression techique. You can check this out using the performance_test function in run_length.rb, which lets you control "distribution" of bit values in a bit vector, and will give handy statistics for how effective the compression was. I have yet to make an interface for this function, but generally the percent compression effectiveness was proportional to the "distribution factor" of 1s and 0s, as I called it. Check out the code for details.
I've also included a command line interface for "compressing" text files. "Compressing" I put in quotes because it actually converts every ASCII character in a file to binary, then converts this binary string to a run lenth encoded string, so in the end the file isn't really any shorter than the original, and in fact is almost certainly going to be longer. It will encode it though, which is cool and handy if you want to keep the contents of a file secret I guess.
The code overall is small and simple, just something I threw together as an experiment one afternoon. Mostly I was curious about how well such a simple encoder could compress bit vectors, encoding ASCII files was an afterthought that I clearly didn't think through all the way.
The bit vector "0001110011" will be converted to "03322"
The first bit of the encoded string is the first bit of original string, and the next numbers are the number of bits until a switch. So "03322" says:
- Start with a 0
- The next 3 bits are 0
- The next 3 are 1
- The next 2 are 0
- The 2 after that are 1
Pretty simple. The code for encoding and decoding is correspondingly tiny (but I bet it could be tinier).
The interface for encoding text files is structured as follows:
$ ruby file_compress.rb [compress|decompress] inpath outpath
Example, to compress/encode the file test.txt and put the compressed copy at test_compressed.txt, run:
$ ruby file_compress.rb compress test.txt test_compressed.txt
To decode/decompress test_compressed.txt run:
$ ruby file_compress.rb decompress test_compressed.txt test_decompressed.txt
There's no real error checking on this interface, so be careful about modifying files. The interface is still very simple and limited, but it's enough to quickly fire up and encode some files with.
Again, I say "compressed" as the operation, but in reality the compressed file will in all likelyhood be encoded but bigger in terms of bytes than the original. Still, I thought it was a fun little tool to play around with. I might look into actual compression techniques in the future.