Hi all,
This is a follow-up to a thread from March, 2000, where JD Smith had offered
functions for returning indices of the values in one array that are found in
a second array. Perhaps due to a change in what Sort() does with identical
entries, the "ind_int_SORT" function gave erroneous results.
(I'm on IDL 6.1.1, Windows XP Pro, and I get this:
IDL> print,sort([1,1])
1 0
)
Here's a simple fix that lets it work no matter *what* order Sort() puts the
indices of identical entries in. (even if it is inconsistent within a single
call to Sort()!)
=====
;; Return the indices of values in a which exists anywhere in b
;; (one only for repeated values)
function ind_int_SORT, a, b
flag=[replicate(0b,n_elements(a)),replicate(1b,n_elements(b) )]
s=[a,b]
srt=sort(s)
s=s[srt] & flag=flag[srt]
wh=where(s eq shift(s,-1) and flag ne shift(flag, -1),cnt)
if cnt eq 0 then return, -1
return,srt[wh+flag[wh]]
end
=====
The fix is just in the "return..." line, which had read:
return,srt[wh]
... and which for me returned:
IDL> print,ind_int_SORT(['1','2'],['1','2'])
2 3
Here we need to know whether an item in 'srt' came from 'a' or 'b', and we
know that from 'flag'. So now, we get:
IDL> print,ind_int_SORT(['1','2'],['1','2'])
0 1
Note that this doesn't guarantee that the result indices are sorted:
IDL> print,ind_int_SORT(['1','1','2','3'],['1','2','4'])
1 0 2
Hmm, since JD's always did guarantee this (like Where() does it), here's one
more amendment:
=====
;; Return the indices of values in a which exists anywhere in b
;; (one only for repeated values)
function ind_int_SORT, a, b
flag=[replicate(0b,n_elements(a)),replicate(1b,n_elements(b) )]
s=[a,b]
srt=sort(s)
s=s[srt] & flag=flag[srt]
wh=where(s eq shift(s,-1) and flag ne shift(flag, -1),cnt)
if cnt eq 0 then return, -1
result=srt[wh+flag[wh]]
return,result[sort(result)]
end
=====
Mark Fardal posted a version of this with a different calling sequence,
here's the amended version of that (two changes, for a_ind and b_ind):
=====
pro listmatch, a, b, a_ind, b_ind
flag=[replicate(0b,n_elements(a)),replicate(1b,n_elements(b) )]
s=[a,b]
srt=sort(s)
s=s[srt] & flag=flag[srt]
wh=where(s eq shift(s,-1) and flag ne shift(flag, -1),cnt)
if cnt ne 0 then begin
a_ind = srt[wh+flag[wh]]
a_ind = a_ind[sort(a_ind)]
b_ind = srt[wh+1-flag[wh]]-N_Elements(a)
b_ind = b_ind[sort(b_ind)]
endif else begin
a_ind = -1
b_ind = -1
return
endelse
end
=====
Thanks to JD and Mark for their original work!
Cheers,
--
-Dick
Dick Jackson / dick@d-jackson.com
D-Jackson Software Consulting / http://www.d-jackson.com
Calgary, Alberta, Canada / +1-403-242-7398 / Fax: 241-7392
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