Ian Knopke
Hi,
I'd like to build a histogram, or even just a frequency count of some categorical data from a large database. In a language such as perl I'd do something like this:
my %freq; # hash while (my $item = get_next_from_db()){ $freq{$item}++; }
and then sum the hash values and divide the value of each key by the sum to get the histogram.
Is there an easy way to do the same thing in Haskell? It looked like an easy task but I seem to be having a lot of trouble getting this to work properly, as it doesn't seem to be behaving very lazily. I'm guessing I should be doing something with the State monad, but I'm not very good at using that yet.
I have a package[1] which I'll eventually put up on Hackage for plotting histograms with Chart[2]. The underlying histogram implementation (for homogenous bin widths only) is intended for use with dense data and internally keeps its accumulator in a mutable vector in the ST monad. Feel free to borrow the code (chart-histogram/Numeric/Histogram.hs). Cheers, - Ben [1] https://github.com/bgamari/chart-histogram [2] http://hackage.haskell.org/package/Chart