| Re: All twisted up over reverse indices! [message #94005 is a reply to message #94003] |
Mon, 19 December 2016 12:45  |
penteado
Messages: 866
Registered: February 2018
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Senior Member
Administrator |
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In case anyone is wondering, the reverse indices can be converted into lists or hashes, which make their use much simpler, with
h=histogram(array,_strict_extra=_ex,reverse_indices=ri,locat ions=locations)
if arg_present(rl) then begin
rl=list(length=n_elements(h))
foreach el,h,i do if (el gt 0L) then rl[i]=ri[ri[i]:ri[i+1]-1]
endif
if arg_present(rh) then begin
rh=!version.release ge '8.3' ? orderedhash(locations) : hash(locations)
foreach el,h,i do if (el gt 0L) then rh[locations[i]]=ri[ri[i]:ri[i+1]-1]
endif
This is used in my histogram wrapper, histogram_pp (http://www.ppenteado.net/idl/pp_lib/doc/histogram_pp.html):
vals=randomu(0L,15)*13d0
h=histogram_pp(vals,reverse_indices=ri,reverse_list=rl,locat ions=loc,reverse_hash=rh)
print,h
;1 3 0 4 2 1 0 4
print,ri[ri[0]:ri[1]-1]
;13
foreach el,rl,i do print,i,' : ',el
;0 : 13
;1 : 8 11 12
;2 : !NULL
;3 : 0 1 4 6
;4 : 9 10
;5 : 2
;6 : !NULL
;7 : 3 5 7 14
foreach el,loc do print,el,' : ',rh[el]
;3.8679500 : 13
;4.8679500 : 8 11 12
;5.8679500 : !NULL
;6.8679500 : 0 1 4 6
;7.8679500 : 9 10
;8.8679500 : 2
;9.8679500 : !NULL
;10.867950 : 3 5 7 14
On Monday, December 19, 2016 at 9:37:46 AM UTC-8, Stephen Williams wrote:
>>
>> I found this helped (scroll down to the section on reverse indices):
>> http://www.idlcoyote.com/tips/histogram_tutorial.html
>
> For completeness, I figured out the problem and determined how to extract what I needed. My issue came primarily from improper referencing of the arrays. For example, the following line gave the incorrect indices when used with multiple matches:
>
> ra_i_m(i) = ra_i(match1[match1[part_two(i)]:match1[part_two(i+1)]-1])
>
> The problem is in the end, and should be this:
>
> ra_i_m(i) = ra_i(match1[match1[part_two(i)]:match1[part_two(i)+1]-1])
>
> The parentheses are critical here, as I want the next array element in "match1" and not the next array element in "part_two".
>
> Distances were obtained similarly via the following line:
>
> d(match1[match1[part_thr(i)]:match1[part_thr(i)+1]-1])
>
> That is to say, the above gives the distances for each element in the sub-array denoted by the ":".
>
> I hope this may help someone, I am sure relieved that my problem has been solved.
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