NAME: MATCH PURPOSE: Routine to match values in two vectors. CALLING SEQUENCE: match, a, b, suba, subb, [ COUNT =, /SORT ] INPUTS: a,b - two vectors to match elements, numeric or string datatype OUTPUTS: suba - subscripts of elements in vector a with a match in vector b subb - subscripts of the positions of the elements in vector b with matchs in vector a. suba and subb are ordered such that a[suba] equals b[subb] OPTIONAL INPUT KEYWORD: /SORT - By default, MATCH uses two different algorithm: (1) the /REVERSE_INDICES keyword to HISTOGRAM is used for integer data, while a sorting algorithm is used for non-integer data. The histogram algorithm is usually faster, except when the input vectors are sparse and contain very large numbers, possibly causing memory problems. Use the /SORT keyword to always use the sort algorithm. OPTIONAL KEYWORD OUTPUT: COUNT - set to the number of matches, integer scalar SIDE EFFECTS: The obsolete system variable !ERR is set to the number of matches; however, the use !ERR is deprecated in favor of the COUNT keyword RESTRICTIONS: The vectors a and b should not have duplicate values within them. You can use rem_dup function to remove duplicate values in a vector EXAMPLE: If a = [3,5,7,9,11] & b = [5,6,7,8,9,10] then IDL> match, a, b, suba, subb, COUNT = count will give suba = [1,2,3], subb = [0,2,4], COUNT = 3 and suba[a] = subb[b] = [5,7,9] METHOD: For non-integer data types, the two input vectors are combined and sorted and the consecutive equal elements are identified. For integer data types, the /REVERSE_INDICES keyword to HISTOGRAM of each array is used to identify where the two arrays have elements in common. HISTORY: D. Lindler Mar. 1986. Fixed "indgen" call for very large arrays W. Landsman Sep 1991 Added COUNT keyword W. Landsman Sep. 1992 Fixed case where single element array supplied W. Landsman Aug 95 Converted to IDL V5.0 W. Landsman September 1997 Use a HISTOGRAM algorithm for integer vector inputs for improved performance W. Landsman March 2000 Work again for strings W. Landsman April 2000