setdiff - Find set difference of two arrays

Syntax

Description

Examples

Difference of Two Vectors

A = [3 6 2 1 5 1 1]; B = [2 4 6];
C = setdiff(A,B)

C =

     1     3     5

Find the Difference of Two Vectors and the Indices to the Different Values

A = [3 6 2 1 5 1 1]; B = [2 4 6];
[C,ia] = setdiff(A,B)

C =

     1     3     5

ia =

     7     1     5

Difference of the Rows in Two Matrices

A = [7 9 7; 0 0 0; 7 9 7; 5 5 5; 1 4 5];
B = [0 0 0; 5 5 5];
[C,ia] = setdiff(A,B,'rows')

C =

     1     4     5
     7     9     7

ia =

     5
     3

Difference of Two Vectors with Specified Output Order

Use the setOrder argument to specify the ordering of the values in C.

Specify 'stable' or 'sorted' when the order of the values in C are important.

A = [3 6 2 1 5 1 1]; B = [2 4 6];
[C,ia] = setdiff(A,B,'stable')

C =

     3     1     5

ia =

     1
     4
     5

Alternatively, you can specify 'sorted' order.

 [C,ia] = setdiff(A,B,'sorted')

C =

     1     3     5

ia =

     4
     1
     5

setdiff adopts the forthcoming behavior when you specify the setOrder argument. If you omit the setOrder argument, the output is sorted, but the size and content of C and ia conforms to the current behavior.

Assessing the Impact of the Forthcoming Changes to setdiff

Use the 'R2012a' flag to assess the impact of the forthcoming behavior changes. Use the 'legacy' flag to preserve the current behavior of your existing code.

Find the difference of A and B with the current default behavior.

A = [3 6 2 1 5 1 1]; B = [2 4 6];
[C1,ia1] = setdiff(A,B)

C1 =

     1     3     5

ia1 =

     7     1     5

Find the difference of A and B, and adopt the forthcoming behavior. In the future, this behavior will be the default.

[C2,ia2] = setdiff(A,B,'R2012a')

C2 =

     1     3     5

ia2 =

     4
     1
     5

Notice that ia1 and ia2 have different shapes and content.

Find the difference of A and B, and preserve the current behavior.

[C3,ia3] = setdiff(A,B,'legacy')

C3 =

     1     3     5

ia3 =

     7     1     5

C3 and ia3 match C1 and ia1.

Find the Difference of Vectors Containing NaNs

A = [5 NaN NaN]; B = [5 NaN];
C = setdiff(A,B)

C =

   NaN   NaN

setdiff treats NaN values as distinct.

Input Arguments

A,B	Input Arrays Vectors | Matrices | N-D Arrays Input arrays can be logical, char, a cell array of strings, or any numeric class. A and B also can be any object with the class methods: sort (or sortrows for the 'rows' option), eq, and ne. This includes heterogeneous arrays derived from the same root class. A and B must be of the same class with the following exceptions: logical, char, and all numeric classes can combine with double arrays. Cell arrays of strings can combine with char arrays. If you specify the 'rows' option, A and B must have the same number of columns. Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical Complex Support: Yes
'rows'	Rows Flag Rows flag, specified as 'rows', identifies the rows of A and B as individual elements. When you specify this flag, setdiff returns the rows from A that are not in B. The arrays, A and B, must have the same number of columns when you use the rows flag. This option does not support cell arrays.
setOrder	Order Flag 'sorted' | 'stable' Order flag, specified as 'sorted' or 'stable', indicates the order of the values (or rows) in C. Order Flag Meaning 'sorted' The values (or rows) in C, are returned in sorted order. For example: C = setdiff([4 1 3 2],[2 1],'sorted') returns C = [3 4]. 'stable' The values (or rows) in C, are returned in the same order as in A. For example: C = setdiff([4 1 3 2],[2 1],'stable') returns C = [4 3].
'legacy'	Legacy Behavior Flag Legacy behavior flag, when specified, preserves the current behavior. If the new behavior adversely affects your existing code, you can preserve the current behavior by specifying 'legacy' as the final argument.
'R2012a'	Future Behavior Flag Future behavior flag, when specified, adopts the future behavior change. Specify R2012a' as the final argument to see what impact the new behavior has on your existing code.

Output Arguments

C	Difference of A and B Vector | Matrix Difference of A and B is returned as a vector or matrix. C is a vector, unless you specify the 'rows' flag. If 'rows' is specified, C is a matrix containing the rows of A that are not in B.
ia	Index to A Vector Index to A identifies the values (or rows) in A that are not in B. If there is a repeated value (or row) appearing exclusively in A, then ia contains the index to the last occurrence of the value (or row). If you call setdiff with the setOrder or 'R2012a' argument, ia contains the index to the first occurrence of any repeated value (or row) in A.

See Also

intersect | ismember | issorted | setxor | sort | union | unique

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