MATCH

       Routine to match values in two vectors.

       match, a, b, suba, subb, [ COUNT =, /SORT ]

       a,b - two vectors to match elements, numeric or string data types

       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]

       /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.

       COUNT - set to the number of matches, integer scalar

       The obsolete system variable !ERR is set to the number of matches;
       however, the use !ERR is deprecated in favor of the COUNT keyword

       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

       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]

       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.

       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
       Use size(/type)                  W. Landsman         December 2002
       Work for scalar integer input    W. Landsman         June 2003

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