;+
; NAME:
; SETINTERSECTION
;
; PURPOSE:
;
; This function is used to find the intersection between two sets of integers.
;
; AUTHOR:
;
; FANNING SOFTWARE CONSULTING
; David Fanning, Ph.D.
; 1645 Sheely Drive
; Fort Collins, CO 80526 USA
; Phone: 970-221-0438
; E-mail: david@idlcoyote.com
; Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
;
; CATEGORY:
;
; Utilities
;
; CALLING SEQUENCE:
;
; intersection = SetIntersection(set_a, set_b)
;
; RETURN VALUE:
;
; intersection: A vector of values that are found in both set_a and set_b.
;
; ARGUMENTS:
;
; set_a: A vector of integers.
;
; set_b: A vector of integers.
;
; KEYWORDRS:
;
; COUNT: An output variable that contains the number of elements in the intersection vector.
;
; NORESULT: Set this keyword to a value that will be returned from the function
; if no intersection between the two sets of numbers is found. By default, -1.
;
; POSITIONS: And output keyword that will return the positions or locations in A where the values
; in B appear.
;
; INDICIES_A: The indices in vector A where the intersected values appear. Note, this requires
; the intersected points be unique in each vector. The POSITIONS
; keyword will return ALL the positions of the match, even if there are non-unique matches.
;
; INDICIES_B: The indices in vector B where the intersected values appear. This assumes that
; the intersected points are represented uniquely in the A and B vectors.
;
; SUCCESS: An output keyword that is set to 1 if an intersection was found, and to 0 otherwise.
;
; EXAMPLE:
;
; IDL> set_a = [1,2,3,4,5]
; IDL> set_b = [4,5,6,7,8,9,10,11]
; IDL> Print, SetIntersection(set_a, set_b)
; 4 5
;
; See http://www.idlcoyote.com/tips/set_operations.html for other types of set operations.
;
; NOTES:
;
; If you read the Set Operations article pointed to above, you will see quite a lot of
; discussion about what kinds of algorithms are faster than others. The Histogram
; algorithms implemented here are sometimes NOT the fastest algorithms, especially
; for sparse arrays. If this is a concern in your application, please be sure to read
; that article.
;
; MODIFICATION HISTORY:
;
; Written by: David W. Fanning, October 31, 2009, from code originally supplied to the IDL
; newsgroup by Research Systems software engineers.
; Yikes, bug in original code only allowed positive integers. Fixed now. 2 Nov 2009. DWF.
; Fixed a problem when one or both of the sets was a scalar value. 18 Nov 2009. DWF.
; Added a POSITIONS keyword. 30 Nov 2012. DWF.
; Added a COUNT keyword 3 Dec 2012. DWF.
; Added INDICES_A and INDICES_B keywords at R.G. Stockwell's suggestion. 13 Dec 2012. DWF.
;-
;******************************************************************************************;
; Copyright (c) 2009, by Fanning Software Consulting, Inc. ;
; All rights reserved. ;
; ;
; Redistribution and use in source and binary forms, with or without ;
; modification, are permitted provided that the following conditions are met: ;
; ;
; * Redistributions of source code must retain the above copyright ;
; notice, this list of conditions and the following disclaimer. ;
; * Redistributions in binary form must reproduce the above copyright ;
; notice, this list of conditions and the following disclaimer in the ;
; documentation and/or other materials provided with the distribution. ;
; * Neither the name of Fanning Software Consulting, Inc. nor the names of its ;
; contributors may be used to endorse or promote products derived from this ;
; software without specific prior written permission. ;
; ;
; THIS SOFTWARE IS PROVIDED BY FANNING SOFTWARE CONSULTING, INC. ''AS IS'' AND ANY ;
; EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES ;
; OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT ;
; SHALL FANNING SOFTWARE CONSULTING, INC. BE LIABLE FOR ANY DIRECT, INDIRECT, ;
; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED ;
; TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; ;
; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ;
; ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT ;
; (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS ;
; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. ;
;******************************************************************************************;
FUNCTION SetIntersection, set_a, set_b, $
COUNT=count, $
INDICES_A=indices_a, $
INDICES_B=indices_b, $
NORESULT=noresult, $
POSITIONS=positions, $
SUCCESS=success
Compile_Opt StrictArr, DefInt32
; Set up noresult value.
IF N_Elements(noresult) EQ 0 THEN noresult = -1
; Error handling.
Catch, theError
IF theError NE 0 THEN BEGIN
Catch, /CANCEL
void = Error_Message()
success = 0
RETURN, noresult
ENDIF
; Check parameters.
IF N_Params() NE 2 THEN Message, 'Two input parameters or sets are required.'
; The input sets must be integers.
IF (Size(set_a, /TYPE) GT 3) AND (Size(set_a, /TYPE) LT 12) THEN $
Message, 'Set A must be an integer array.'
IF (Size(set_b, /TYPE) GT 3) AND (Size(set_b, /TYPE) LT 12) THEN $
Message, 'Set B must be an integer array.'
; If either of the sets is a scalar, make it a vector.
IF N_Elements(set_a) EQ 1 && (Size(set_a))[0] EQ 0 THEN set_a = [set_a]
IF N_Elements(set_b) EQ 1 && (Size(set_b))[0] EQ 0 THEN set_b = [set_b]
; Assume success.
success = 1
count = 0
; Find the intersection of the ranges.
mina = Min(set_a, Max=maxa)
minb = Min(set_b, Max=maxb)
minab = mina > minb
maxab = maxa < maxb
; If the set ranges don't intersect, leave now.
IF ((maxa LT minab) AND (minb GT maxab)) OR ((maxb LT minab) AND (mina GT maxab)) THEN BEGIN
success = 0
RETURN, noresult
ENDIF
; Find the intersection.
r = Where((Histogram(set_a, Min=minab, Max=maxab, REVERSE_INDICES=ra) NE 0) AND $
(Histogram(set_b, Min=minab, Max=maxab, REVERSE_INDICES=rb) NE 0), count)
; Was there an intersection? If not, leave now.
IF count EQ 0 THEN BEGIN
success = 0
RETURN, noresult
ENDIF
; Do you want the positions in A where B is found?
IF Arg_Present(positions) THEN BEGIN
FOR j=0,N_Elements(r)-1 DO BEGIN
IF N_Elements(thesePositions) EQ 0 THEN BEGIN
thesePositions = [ReverseIndices(ra, r[j])]
ENDIF ELSE BEGIN
thesePositions = [thesePositions, ReverseIndices(ra, r[j])]
ENDELSE
ENDFOR
positions = thesePositions
ENDIF
; Do you want the indices of the matches? Code provided by
; R.G. Stockwell. Note that if you ask for indices, the sets
; may NOT have duplicate values in them. Each value in both sets
; must be unique.
IF Arg_Present(indices_a) || Arg_Present(indices_b) THEN BEGIN
aindices = LonArr(count)
bindices = LonArr(count)
FOR matchCounter=0,count-1 DO BEGIN
j = r[matchCounter]
aindices[matchcounter] = ra[ra[j]:ra[j+1]-1]
bindices[matchcounter] = rb[rb[j]:rb[j+1]-1]
ENDFOR
indices_a = Temporary(aindices)
indices_b = Temporary(bindices)
ENDIF
; Here is the result.
result = Temporary(r) + minab
; Return the result. Make sure to return scalar if only a single element.
IF N_Elements(result) EQ 1 THEN RETURN, result[0] ELSE RETURN, result
END