On Sunday, 23 December 2012 13:56:24 UTC+11, Josh Sixsmith wrote:
> Hi, I'm curious about whether IDL is inclusive or exclusive in regards to the final bin. The help documentation describes that the right hand side of a bin is exclusive, but what about the final bin?
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>
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> For example, using the following sample data
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>
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> a = [ 0.72244781, 0.20885457, 0.38053078, 0.89579923, 0.93703798,$
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> 1. , 0.22754776, 0.11365818, 0.38424101, 0.1741128 ,$
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> 0.63094614, 0.00123615, 0.06025917, 0.78652067, 0.1001857 ,$
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> 0.80492211, 0.80564817, 0.83369342, 0.94378603, 0.75453023]
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>
>
> ha = histogram(a, nbins=10, binsize=0.1, min=0, reverse_indices=ria, locations=loca, omax=omaxa, omin=omina)
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> IDL> print, loca
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> 0.00000 0.10000 0.20000 0.30000 0.40000 0.50000
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> 0.60000 0.70000 0.80000 0.90000
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>
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> IDL> print, ha
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> 2 3 2 2 0 0
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> 1 3 4 3
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>
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> This result looks fine and i interpret the locations as
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>
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> [0,0.1),[0.1,0.2),[0.2,0.3),[0.3,0.4),[0.4,0.5),[0.5,0.6),[0 .6,0.7),[0.7,0.8),
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> [0.8,0.9),[0.9,1.0]
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>
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> indicating the last bin as inclusive as the value of 1.0 is included in the histogram.
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> However i feel that this might actually be a case of misrepresentation of floating point numbers, as mentioned in the example given in http://www.idlcoyote.com/math_tips/razoredge.html
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> If array 'a' is double:
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> ad = double(a)
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> had = histogram(ad, nbins=10, binsize=0.1d, min=0.0d, reverse_indices=riad, locations=locad, omin=ominad, omax=omaxad)
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> print, had
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> 2 3 2 2 0 0
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> 1 3 4 2
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>
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> which suggests that the last bin is exclusive and that all bins are exclusive
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>
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> [0,0.1),[0.1,0.2),[0.2,0.3),[0.3,0.4),[0.4,0.5),[0.5,0.6),[0 .6,0.7),[0.7,0.8),
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> [0.8,0.9),[0.9,1.0)
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>
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> For integer data this also seems to be the case
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> IDL> print, locbHowever, for integer data this doesn't seem to be the case.
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> b = indgen(11)
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> hb = histogram(b, nbins=10, min=0, reverse_indices=rib, locations=locb, omax=omaxb, omin=ominb)
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> IDL> print, locb
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> 0 1 2 3 4 5 6 7 8 9
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> IDL> print, hb
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> 1 1 1 1 1 1
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> 1 1 1 1
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> IDL> print, rib
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> 11 12 13 14 15 16
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> 17 18 19 20 21 0
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> 1 2 3 4 5 6
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> 7 8 9
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> The index '10' for the value 10 is not included
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>
>
> So if i use the max keyword, i would assume that this would be an upper limit of values to be included in the histogram. Does this then make the last bin inclusive, or will it create a bin that will not only include the max value but potentially include values slightly higher than the specified max. This might only occur if the binsize is set.
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> Any clarification would be greatly appreciated.
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>
>
> Cheers
>
> Josh
Great, thanks for that.
I'll keep that in mind for future use.
Cheers
Josh
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