(octave.info)Set Operations

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27.1 Set Operations
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Octave supports several basic set operations.  Octave can compute the
union, intersection, and difference of two sets.  Octave also supports
the _Exclusive Or_ set operation.

   The functions for set operations all work in the same way by
accepting two input sets and returning a third set.  As an example,
assume that ‘a’ and ‘b’ contains two sets, then

     union (a, b)

computes the union of the two sets.

   Finally, determining whether elements belong to a set can be done
with the ‘ismember’ function.  Because sets are ordered this operation
is very efficient and is of order O(log2(n)) which is preferable to the
‘find’ function which is of order O(n).

 -- : C = intersect (A, B)
 -- : C = intersect (A, B, "rows")
 -- : [C, IA, IB] = intersect (...)

     Return the unique elements common to both A and B sorted in
     ascending order.

     If A and B are both row vectors then return a row vector;
     Otherwise, return a column vector.  The inputs may also be cell
     arrays of strings.

     If the optional input "rows" is given then return the common rows
     of A and B.  The inputs must be 2-D matrices to use this option.

     If requested, return index vectors IA and IB such that ‘C = A(IA)’
     and ‘C = B(IB)’.

     See also: Note: unique, Note: union, Note:
     setdiff, Note: setxor, *note ismember:
     XREFismember.

 -- : C = union (A, B)
 -- : C = union (A, B, "rows")
 -- : [C, IA, IB] = union (...)

     Return the unique elements that are in either A or B sorted in
     ascending order.

     If A and B are both row vectors then return a row vector;
     Otherwise, return a column vector.  The inputs may also be cell
     arrays of strings.

     If the optional input "rows" is given then return rows that are in
     either A or B.  The inputs must be 2-D matrices to use this option.

     The optional outputs IA and IB are index vectors such that ‘A(IA)’
     and ‘B(IB)’ are disjoint sets whose union is C.

     See also: Note: unique, Note: intersect,
     Note: setdiff, Note: setxor, Note:
     ismember.

 -- : C = setdiff (A, B)
 -- : C = setdiff (A, B, "rows")
 -- : [C, IA] = setdiff (...)
     Return the unique elements in A that are not in B sorted in
     ascending order.

     If A is a row vector return a row vector; Otherwise, return a
     column vector.  The inputs may also be cell arrays of strings.

     If the optional input "rows" is given then return the rows in A
     that are not in B.  The inputs must be 2-D matrices to use this
     option.

     If requested, return the index vector IA such that ‘C = A(IA)’.

     See also: Note: unique, Note: union, Note:
     intersect, Note: setxor, *note ismember:
     XREFismember.

 -- : C = setxor (A, B)
 -- : C = setxor (A, B, "rows")
 -- : [C, IA, IB] = setxor (...)

     Return the unique elements exclusive to sets A or B sorted in
     ascending order.

     If A and B are both row vectors then return a row vector;
     Otherwise, return a column vector.  The inputs may also be cell
     arrays of strings.

     If the optional input "rows" is given then return the rows
     exclusive to sets A and B.  The inputs must be 2-D matrices to use
     this option.

     If requested, return index vectors IA and IB such that ‘A(IA)’ and
     ‘B(IB)’ are disjoint sets whose union is C.

     See also: Note: unique, Note: union, Note:
     intersect, Note: setdiff, Note:
     ismember.

 -- : TF = ismember (A, S)
 -- : TF = ismember (A, S, "rows")
 -- : [TF, S_IDX] = ismember (...)

     Return a logical matrix TF with the same shape as A which is true
     (1) if the element in A is found in S and false (0) if it is not.

     If a second output argument is requested then the index into S of
     each matching element is also returned.

          a = [3, 10, 1];
          s = [0:9];
          [tf, s_idx] = ismember (a, s)
               ⇒ tf = [1, 0, 1]
               ⇒ s_idx = [4, 0, 2]

     The inputs A and S may also be cell arrays.

          a = {"abc"};
          s = {"abc", "def"};
          [tf, s_idx] = ismember (a, s)
               ⇒ tf = [1, 0]
               ⇒ s_idx = [1, 0]

     If the optional third argument "rows" is given then compare rows in
     A with rows in S.  The inputs must be 2-D matrices with the same
     number of columns to use this option.

          a = [1:3; 5:7; 4:6];
          s = [0:2; 1:3; 2:4; 3:5; 4:6];
          [tf, s_idx] = ismember (a, s, "rows")
               ⇒ tf = logical ([1; 0; 1])
               ⇒ s_idx = [2; 0; 5];

     See also: Note: lookup, Note: unique, Note:
     union, Note: intersect, *note setdiff:
     XREFsetdiff, Note: setxor.

 -- : powerset (A)
 -- : powerset (A, "rows")
     Compute the powerset (all subsets) of the set A.

     The set A must be a numerical matrix or a cell array of strings.
     The output will always be a cell array of either vectors or
     strings.

     With the optional argument "rows", each row of the set A is
     considered one element of the set.  The input must be a 2-D numeric
     matrix to use this argument.

     See also: Note: unique, Note: union, Note:
     intersect, Note: setdiff, *note setxor:
     XREFsetxor, Note: ismember.