setdiff

Set difference of two arrays

Description

example

C = setdiff(A,B) returns the data in A that is not in B, with no repetitions. C is in sorted order.

• If A and B are tables or timetables, then setdiff returns the rows from A that are not in B. For timetables, setdiff takes row times into account to determine equality, and sorts the output timetable C by row times.

example

C = setdiff(A,B,setOrder) returns C in a specific order. setOrder can be 'sorted' or 'stable'.

C = setdiff(A,B,___,'rows') and C = setdiff(A,B,'rows',___) treat each row of A and each row of B as single entities and return the rows from A that are not in B, with no repetitions. You must specify A and B and optionally can specify setOrder.

The 'rows' option does not support cell arrays, unless one of the inputs is either a categorical array or a datetime array.

example

[C,ia] = setdiff(___) also returns the index vector ia using any of the previous syntaxes.

• Generally, C = A(ia).

• If the 'rows' option is specified, then C = A(ia,:).

• If A and B are tables or timetables, then C = A(ia,:).

example

[C,ia] = setdiff(A,B,'legacy') and [C,ia] = setdiff(A,B,'rows','legacy') preserve the behavior of the setdiff function from R2012b and prior releases.

The 'legacy' option does not support categorical arrays, datetime arrays, duration arrays, tables, or timetables.

Examples

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Define two vectors with values in common.

A = [3 6 2 1 5 1 1];
B = [2 4 6];

Find the values in A that are not in B.

C = setdiff(A,B)
C = 1×3

1     3     5

Define two tables with rows in common.

A = table([1:5]',['A';'B';'C';'D';'E'],logical([0;1;0;1;0]))
A=5×3 table
Var1    Var2    Var3
____    ____    _____

1       A      false
2       B      true
3       C      false
4       D      true
5       E      false

B = table([1:2:10]',['A';'C';'E';'G';'I'],logical(zeros(5,1)))
B=5×3 table
Var1    Var2    Var3
____    ____    _____

1       A      false
3       C      false
5       E      false
7       G      false
9       I      false

Find the rows in A that are not in B.

C = setdiff(A,B)
C=2×3 table
Var1    Var2    Var3
____    ____    _____

2       B      true
4       D      true

Define two vectors with values in common.

A = [3 6 2 1 5 1 1];
B = [2 4 6];

Find the values in A that are not in B as well as the index vector ia, such that C = A(ia).

[C,ia] = setdiff(A,B)
C = 1×3

1     3     5

ia = 3×1

4
1
5

Define a table, A, of gender, age, and height for five people.

A = table(['M';'M';'F';'M';'F'],[27;52;31;46;35],[74;68;64;61;64],...
'VariableNames',{'Gender' 'Age' 'Height'},...
'RowNames',{'Ted' 'Fred' 'Betty' 'Bob' 'Judy'})
A=5×3 table
Gender    Age    Height
______    ___    ______

Ted        M       27       74
Fred       M       52       68
Betty      F       31       64
Bob        M       46       61
Judy       F       35       64

Define a table, B, with the same variables as A.

B = table(['F';'M';'F';'F'],[64;68;62;58],[31;47;35;23],...
'VariableNames',{'Gender' 'Height' 'Age'},...
'RowNames',{'Meg' 'Joe' 'Beth' 'Amy'})
B=4×3 table
Gender    Height    Age
______    ______    ___

Meg       F         64      31
Joe       M         68      47
Beth      F         62      35
Amy       F         58      23

Find the rows in A that are not in B, as well as the index vector ia, such that C = A(ia,:).

[C,ia] = setdiff(A,B)
C=4×3 table
Gender    Age    Height
______    ___    ______

Judy      F       35       64
Ted       M       27       74
Bob       M       46       61
Fred      M       52       68

ia = 4×1

5
1
4
2

The rows of C are in sorted order first by Gender and next by Age.

Define two matrices with rows in common.

A = [7 9 7; 0 0 0; 7 9 7; 5 5 5; 1 4 5];
B = [0 0 0; 5 5 5];

Find the rows from A that are not in B as well as the index vector ia, such that C = A(ia,:).

[C,ia] = setdiff(A,B,'rows')
C = 2×3

1     4     5
7     9     7

ia = 2×1

5
1

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 = 1×3

3     1     5

ia = 3×1

1
4
5

Alternatively, you can specify 'sorted' order.

[C,ia] = setdiff(A,B,'sorted')
C = 1×3

1     3     5

ia = 3×1

4
1
5

Define two vectors containing NaN.

A = [5 NaN NaN];
B = [5 NaN];

Find the set difference of A and B.

C = setdiff(A,B)
C = 1×2

NaN   NaN

setdiff treats NaN values as distinct.

Create a cell array of character vectors, A.

A = {'dog','cat','fish','horse'};

Create a cell array of character vectors, B, where some of the vectors have trailing white space.

B = {'dog ','cat','fish ','horse'};

Find the character vectors in A that are not in B.

[C,ia] = setdiff(A,B)
C = 1x2 cell
{'dog'}    {'fish'}

ia = 2×1

1
3

setdiff treats trailing white space in cell arrays of character vectors as distinct characters.

Create a character vector, A.

A = ['cat';'dog';'fox';'pig'];
class(A)
ans =
'char'

Create a cell array of character vectors, B.

B={'dog','cat','fish','horse'};
class(B)
ans =
'cell'

Find the character vectors in A that are not in B.

C = setdiff(A,B)
C = 2x1 cell
{'fox'}
{'pig'}

The result, C, is a cell array of character vectors.

class(C)
ans =
'cell'

Use the 'legacy' flag to preserve the behavior of setdiff from R2012b and prior releases in your code.

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

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

1     3     5

ia1 = 3×1

4
1
5

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

[C2,ia2] = setdiff(A,B,'legacy')
C2 = 1×3

1     3     5

ia2 = 1×3

7     1     5

Input Arguments

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Input arrays. If you specify the 'rows' option, then A and B must have the same number of columns.

A and B must belong to the same class with the following exceptions:

• logical, char, and all numeric classes can combine with double arrays.

• Cell arrays of character vectors can combine with character arrays or string arrays.

• Categorical arrays can combine with character arrays, cell arrays of character vectors, or string arrays.

• Datetime arrays can combine with cell arrays of date character vectors or single date character vectors.

There are additional requirements for A and B based on data type:

• If A and B are both ordinal categorical arrays, they must have the same sets of categories, including their order. If neither A nor B are ordinal, they need not have the same sets of categories, and the comparison is performed using the category names. In this case, the categories of C consist of the categories of A followed by the categories of B that are not in A. The categories are in the same order as in A and B, and the category order is used for sorting C.

• If A and B are tables or timetables, they must have the same variable names (except for order). For tables, row names are ignored, so that two rows that have the same values, but different names, are considered equal. For timetables, row times are taken into account, so that two rows that have the same values, but different times, are not considered equal.

• If A and B are datetime arrays, they must be consistent with each other in whether they specify a time zone.

A and B also can be objects with the following class methods:

• sort (or sortrows for the 'rows' option)

• eq

• ne

The object class methods must be consistent with each other. These objects include heterogeneous arrays derived from the same root class. For example, A and B can be arrays of handles to graphics objects.

Order flag, specified as 'sorted' or 'stable', indicates the order of the values (or rows) in C.

FlagDescription
'sorted'

The values (or rows) in C return in sorted order as returned by sort.

Example

C = setdiff([4 1 3 2 5],[2 1],'sorted')
C =

3     4     5

'stable'

The values (or rows) in C return in the same order as in A.

Example

C = setdiff([4 1 3 2 5],[2 1],'stable')
C =

4     3     5

Data Types: char | string

Output Arguments

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Difference of A and B, returned as a vector, matrix, table, or timetable. If the inputs A and B are tables or timetables, then the order of the variables in C is the same as the order of the variables in A.

The following describes the shape of C when the inputs are vectors or matrices and when the 'legacy' flag is not specified:

• If the 'rows' flag is not specified and A is a row vector, then C is a row vector.

• If the 'rows' flag is not specified and A is not a row vector, then C is a column vector.

• If the'rows' flag is specified, then C is a matrix containing the rows of A that are not in B.

• If all the values (or rows) of A are also in B, then C is an empty matrix.

The class of C is the same as the class of A, unless:

• A is a character array and B is a cell array of character vectors, in which case C is a cell array of character vectors.

• A is a character vector, cell array of character vectors, or string, and B is a categorical array, in which case C is a categorical array.

• A is a cell array of character vectors or single character vector and B is a datetime array, in which case C is a datetime array.

• A is a character vector or cell array of character vectors and B is a string array, in which case C is a string array.

Index to A, returned as a column vector when the 'legacy' flag is not specified. ia 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 first occurrence of the value (or row).

Tips

• To find the set difference with respect to a subset of variables from a table or timetable, you can use column subscripting. For example, you can use setdiff(A(:,vars),B(:,vars)), where vars is a positive integer, a vector of positive integers, a variable name, a cell array of variable names, or a logical vector. Alternatively, you can use vartype to create a subscript that selects variables of a specified type.