| Re: Histogram and bin sizes [message #58773 is a reply to message #58772] |
Thu, 21 February 2008 08:29   |
jeffnettles4870
Messages: 111
Registered: October 2006
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Senior Member |
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On Feb 21, 9:05 am, Conor <cmanc...@gmail.com> wrote:
> On Feb 20, 2:43 pm, pgri...@gmail.com wrote:
>
>
>
>> jeffnettles4...@gmail.com wrote:
>>> I've always wondered why you have to use a constant bin size with
>>> HISTOGRAM().
>>> To quote J.D.'s famous tutorial: "a histogram
>>> represents nothing more than a fancy way to count." Doesn't an
>>> imposed constant bin size imply that this is the only way it's ok to
>>> count? I can think of several reasons i wouldn't want to do this - I
>>> used logarithmic bin sizes in my dissertation, for example (now i'm
>>> hoping someone isn't going to answer this post saying i screwed up in
>>> my dissertation :-) ).
>
>> I use logarithmic bins myself quite often, and the fact that a
>> logarithmic bin
>> size is the same as a constant bin size in log space, makes it is easy
>> to use histogram to get that. Less regulars binning don't work with
>> histogram, but nobody stops you from writing your own version to work
>> with them (it will not be as fast as histogram though).
>
>> Ciao,
>> Paolo
>
>>> And besides, Excel lets you use arbitrary bin
>>> sizes....and if Excel lets you do it, it has to be ok, right???? ;-)
>
>>> Jeff
>
> You can always do whatever binning you want, you just have to
> transform your data to the new space and then bin it constantly. Why
> doesn't histogram let you use aribtrary binsizes? Not being an IDL
> developer I don't know for sure, but I would guess it's a speed
> issue. The simpler a program is the faster it is. I use histogram
> all the time because it's one of the speedier programs in IDL. It
> would make me very sad if in order to make histogram more flexible, it
> also became much slower, especially since by transforming my data set
> I can use aribtrary bin sizes for histogram.
That actually sounds like what i've done in the past. For my
dissertation i needed two kinds of histograms: logarithmic bins
(which was fine, no trouble there) and bins that had arbitrary sizes.
For the latter, i would either do the histograms in Excel (yuck) or
compute two or three histograms in IDL using histogram() with
different bin sizes and sort of do some "mixing and matching" of the
resulting arrays to get what i wanted. Of course, David hadn't
written his awesome histoplot routine yet then either :( Anyway, i'm
up against the arbitrary bin sizes problem again for a project i'm
doing for someone, and it got me wondering whether this situation is
just so rare it wasn't worth supporting in histogram(). I wouldn't
want to lose histogram's speed either though.
Jeff
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