I think it would be nice to have a histogram function for NArray.

Let's say you have an NArray of integer values:

a = NArray.to_na([1,1,1,1,2,2,2,2,2,3,3,3,4])

You would like to know the distribution of data in your NArray. Having a histogram function would be useful:

h = a.histogram
=> {1=>4, 2=>5, 3=>3, 4=>1}

Perhaps there are other ideas for how to return the result, but one way would be to return it in a hash with value (bin) as key and occurances (frequency) as value.

Do you think it is a good idea for NArray?