most elegant functional way to make a histogram

[Meta via Digitalmars-d-learn]

On Saturday, 22 August 2015 at 02:12:41 UTC, BBasile wrote:
> On Friday, 21 August 2015 at 20:09:22 UTC, Laeeth Isharc wrote:
>> I have four arrays of ints, each array representing a kind of 
>> event associated with that int (they all map to the same 
>> space).  Each array might have the same number multiple times 
>> and each array will be of different length.
>>
>> So I would like to plot the int line on x axis and show number 
>> of times that the number occurs for each array (4 bars for 
>> each int).
>>
>> It's easy to do with loops, but what's best 
>> functional/algorithmic way, please?  Brain tired today.  I am 
>> trying to use these opportunities to learn the algorithmic way 
>> even if loop is more natural.
>>
>> I could just make four new arrays of ints and use each instead 
>> of a loop.  Any better way?
>>
>> Also, for bucketizing, any thoughts on best way to do using 
>> phobos?  (Cos probably I have too many ints and need to 
>> bracket them to plot a histogram).
>>
>> Sorry if this is unclear.
>>
>>
>> Laeeth.
>
> loop-less approach, it consumes an InputRange in a recursive 
> function.
> Assuming histogramData is a custom InputRange:
>
> ---
> void upperLevel()
> {
>     //histogramData = ...
>     proc(histogramData);
>     // continue once the range is consumed
> }
>
> void proc(ref histogramData)
> {
>     //something with front
>     histogramData.popFront;
>     if (!histogramData.empty)
>         proc(histogramData);
> }
> ---
>
> I don't know if this approach can be used but this is an 
> alternative to loops.
> Not necessarily the best because local variables in proc() can 
> lead to a stack overflow.

I believe in your example the compiler will perform TCO so you 
should be okay.