;+ ; 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