| Re: The intersection of 2 arrays [message #8448 is a reply to message #8357] |
Tue, 04 March 1997 00:00  |
Marty Ryba
Messages: 16
Registered: May 1996
|
Junior Member |
|
|
This is a multi-part message in MIME format.
--------------2E7B149D1BEF
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Phil Williams wrote:
> But how would I go about finding the intersection of the two arrays?
> i.e. Is there a nice vector way of doing it rather than brute force?
> (aka: Which IDL function did I miss this time?)
I don't know if this is *exactly* what you are looking for, but the
algorithm should be useful. This is SYNCHRONIZE, which will find the
intersection of two arrays of structures based on matching values of a
specified tag name. I use it often in our data analysis. Many thanks
go to David Stern of RSI for the algorithm.
--
Dr. Marty Ryba | Of course nothing I say here is official
MIT Lincoln Laboratory | policy, and Laboratory affililaton is
ryba@ll.mit.edu | for identification purposes only,
| blah, blah, blah, ...
--------------2E7B149D1BEF
Content-Type: text/plain; charset=us-ascii; name="synchronize.pro"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline; filename="synchronize.pro"
;+
; Name:
; SYNCHRONIZE
; Purpose:
; Match up two arrays of structures by a tag name
; Usage:
; synchonize,a,b[,ause=ause][,buse=buse][,keywords=values]
; Inputs:
; A & B are arrays of structures to be sychronized. They are
; returned containing only those members that match within the
; specified tolerance for the tag fields being matched.
; Optional Keyword Inputs:
; tags - String array containing the tag names to match by. Defaults
; to ['dwell','dwell']. Case insensitive.
; tolerance - Maximum difference to declare a match. All comparisions
; are double precision. Defaults to 0.0 (exact match).
; Optional Outputs:
; ause - Set of array indicies used to convert input A to output A.
; Useful if you have 2 already synchonized arrays and need to
; synch a third.
; buse - Same for B
; Restrictions:
; The structures should have only one member with the tag name given.
; If there are multiple structure members with the same tag, SYNCHRONIZE
; will use the first.
; Cannot use tags from nested structures.
; Modification History:
; M.F. Ryba, MIT/LL, June 93, Created from algorithm written by David
; Stern of RSI.
; M.F. Ryba, Jan 95, added TEMPORARY and check for whether the
; structure is shortened.
;-
PRO Synchronize, a, b, ause=ause, buse=buse, tags=tags, tolerance=tolerance, $
help=help
IF keyword_set(help) THEN BEGIN
doc_library, 'synchronize'
return
ENDIF
IF n_elements(tags) EQ 0 THEN tags = ['dwell', 'dwell']
IF n_elements(tolerance) EQ 0 THEN tolerance = 0.0d
tags = strupcase(tags)
atags = tag_names(a)
btags = tag_names(b)
ai = where(atags EQ tags(0), cnt)
IF cnt EQ 0 THEN BEGIN
string = 'Tag '+tags(0)+' not found in structure A'
message, string
ENDIF
IF cnt GT 1 THEN BEGIN
string = 'Structure A has more than 1 tag named '+tags(0)+ $
'; will use the first'
message, string, /informational
ENDIF
bi = where(btags EQ tags(1), cnt)
IF cnt EQ 0 THEN BEGIN
string = 'Tag '+tags(1)+' not found in structure B'
message, string
ENDIF
IF cnt GT 1 THEN BEGIN
string = 'Structure B has more than 1 tag named '+tags(1)+ $
'; will use the first'
message, string, /informational
ENDIF
ai = ai(0) & bi = bi(0)
tmp = [double(a.(ai)), double(b.(bi))]
sortab = sort(tmp)
tmp = tmp(sortab)
match = where((tmp(1:*) - tmp) LE tolerance, cnt)
IF cnt GT 0 THEN BEGIN
aeq = sortab(match)
beq = sortab(match+1)
tmp = aeq < beq
beq = (beq > aeq) - n_elements(a)
aeq = tmp
IF n_elements(aeq) NE n_elements(a) THEN a = (temporary(a))(aeq)
IF n_elements(beq) NE n_elements(b) THEN b = (temporary(b))(beq)
ause = aeq
buse = beq
ENDIF ELSE BEGIN
print, 'No matches found between A.'+tags(0)+' and B.'+tags(1)
ause = -1
buse = -1
ENDELSE
return
END
--------------2E7B149D1BEF--
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
