Comments on: Generating all combinations of n elements taken t at a time http://www.riondabsd.net/2012/03/08/generating-all-combinations-of-n-elements-taken-t-at-a-time/ A hard working wasp in the big garden of the Internet Fri, 08 Mar 2013 18:51:08 +0000 hourly 1 http://wordpress.org/?v=3.5.1 By: Matteo http://www.riondabsd.net/2012/03/08/generating-all-combinations-of-n-elements-taken-t-at-a-time/comment-page-1/#comment-69514 Matteo Fri, 09 Mar 2012 23:56:01 +0000 http://www.riondabsd.net/?p=2930#comment-69514 Sure. You call it as “./chaseseqcombgen n t” and it will print to stdout the bitstrings (i.e. strings of zeroes and ones) corresponding to the combinations of n elements taken t at a time. Each printed line corresponds to a combination. Each combination is a string of n characters, of which t are ones, and n-t are zeroes. A “1″ in position i (0 less or equal than i less or equal than n-1) means that element “i” (in some predefined order of the elements) appears in the combination. A “0″ means that the element does not.

I personally use it as a key-generating step in a Hadoop MapReduce algorithm. I need to create all combinations of n items and associate a unique key to each combination. This does the job of creating the unique key and at the same time telling me exactly which items belong to the combination.

I believe it can be useful if you modify the code so that, instead of printing the combination bitstring, you do something with the combination, e.g., it’s a good place to actually build the combination.

]]> By: Marcus Reid http://www.riondabsd.net/2012/03/08/generating-all-combinations-of-n-elements-taken-t-at-a-time/comment-page-1/#comment-69510 Marcus Reid Fri, 09 Mar 2012 21:18:11 +0000 http://www.riondabsd.net/?p=2930#comment-69510 Can you give an example of its use?

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