| Bug: HISTOGRAM with reverse indices AND NaN [message #18412] |
Thu, 23 December 1999 00:00 |
Paul Krummel
Messages: 12
Registered: August 1998
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Junior Member |
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Hi All,
I just submitted this as a bug report to RSI.
I use IDL 5.3 (and 5.2) on a windows NT 4 SP5 platform.
I have been using the histogram procedure with reverse_indices to perform
bin averaging for quite a few years now.
Recently I had some data with NaN's in it so I implemented the NaN keyword.
I started getting screwy results. If there were a large number of NaN's my
averaging routine would fall over due to an incorrect indice in the
reverse_indice itself (see below).
Anyway thought you might be interested in this!
Cheers Paul
----------------------------------------------------
I am running IDL 5.3 on the platform mentioned above.
I have discovered what I think is a bug in the histogram function.
It occurs when using the reverse_indices keyword AND the NaN keyword.
The reverse indices that are returned are incorrect if there is missing data
(NaN).
The procedure below should demonstrate this. I also tested this on an SGI
running IRIX 6.5 and IDL 5.2.
; ++
pro hist_ri_fail
;
; ++++
; quick procedure to demonstrate where the
; histogram reverse indices fail when data
; contains NaNs. Counter not incremented
; correctly?.
;
; PBK 23 Dec 1999.
;
; ++++
; make an array
a=findgen(100)
;
; Set every 3rd point to NaN
a[where(a mod 3 eq 0.)]=!values.f_nan
;
print,'a:',a
;
; do the histogram and return reverse indices.
count_mid=histogram(a, binsize=10, reverse_indices=r, $
min=0., max=99., /NaN)
;
; ++++
; find number of Nan's and print some values
zz=where(finite(a,/nan), cnt_nan)
print,'cnt nan:',cnt_nan
print,'cnt mid:',count_mid
print,'n rev ind:',n_elements(r)
print,'rev ind:',r
;
; ++++
end
; ++
a: NaN 1.00000 2.00000 NaN 4.00000
5.00000 NaN 7.00000 8.00000 NaN 10.0000
11.0000 NaN 13.0000 14.0000 NaN 16.0000
17.0000 NaN 19.0000 20.0000 NaN 22.0000
23.0000 NaN 25.0000 26.0000 NaN 28.0000
29.0000 NaN 31.0000 32.0000 NaN 34.0000
35.0000 NaN 37.0000 38.0000 NaN 40.0000
41.0000 NaN 43.0000 44.0000 NaN 46.0000
47.0000 NaN 49.0000 50.0000 NaN 52.0000
53.0000 NaN 55.0000 56.0000 NaN 58.0000
59.0000 NaN 61.0000 62.0000 NaN 64.0000
65.0000 NaN 67.0000 68.0000 NaN 70.0000
71.0000 NaN 73.0000 74.0000 NaN 76.0000
77.0000 NaN 79.0000 80.0000 NaN 82.0000
83.0000 NaN 85.0000 86.0000 NaN 88.0000
89.0000 NaN 91.0000 92.0000 NaN 94.0000
95.0000 NaN 97.0000 98.0000 NaN
cnt nan: 34
cnt mid: 6 7 7 6 7
7 6 7 7 6
n rev ind: 77
rev ind: 11 51 24 31 37
44 51 57 64 71 77
0 1 2 3 4 5
10 11 13 14 16 17
19 21 24 27 30 33
36 39 42 45 48 51
54 57 60 63 66 69
72 75 78 81 84 87
90 93 96 99 61 62
64 65 67 68 70 71
73 74 76 77 79 80
82 83 85 86 88 89
91 92 94 95 97 98
From the output you will see that the reverse indices are not correct and
quite screwy!
The second number of the reverse indices should be 17 not 51 (17+34), so the
count of the number of NaN's has been added to this second indice. The rest
of the pointer numbers (first 11 elements of r for this case) look fine.
The first 6 actual indices (r[11:16]) are wrong, it appears to be just 0 to
5!
The next 7 indices (r[17:23]) are correct!
Then, most of the NaN indices are listed (r[24:50], 50=24+34-7-1).
The rest of the indices are correct.
There is no way to recover all the correct indices from this. The output
from histogram itself (count_mid in the example) appears to be fine. The
toal number of reverse indices (77) is also correct, but as shown above the
indices themselves are incorrect.
Cheers Paul
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~- ~-~-~-~
Paul Krummel
CSIRO Atmospheric Research - GASLAB
Private Bag #1 Aspendale Victoria 3195 Australia
e-mail: paul.krummel@dar.csiro.au www: http://www.dar.csiro.au/
tel: +61 3 9239 4568 fax: +61 3 9239 4444
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~- ~-~-~-~
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