setdiff

Set difference of two arrays

Syntax

C = setdiff(A,B)

C = setdiff(A,B,setOrder)

C = setdiff(A,B,___,'rows')

C = setdiff(A,B,'rows',___)

[C,ia] = setdiff(___)

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

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

Description

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.

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.

[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,:).

[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

Difference of Two Vectors

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

Difference of Two Tables

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 

Difference of Two Vectors and Indices to Different Values

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

Difference of Two Tables and Indices to Different Rows

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.

Difference of Rows in Two Matrices

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

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 = 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

Difference of Vectors Containing NaNs

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.

Cell Array of Character Vectors with Trailing White Space

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.

Difference of Char and Cell Array of Character Vectors

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'

Preserve Legacy Behavior of setdiff

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

A,B — Input arrays

numeric arrays | logical arrays | character arrays | string arrays | categorical arrays | datetime arrays | duration arrays | cell arrays of character vectors | tables | timetables

Input arrays, specified as numeric arrays, logical arrays, character arrays, string arrays, categorical arrays, datetime arrays, duration arrays, cell arrays of character vectors, tables, or timetables. If you specify the 'rows' option, 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 are the sorted union of the categories from A and B.

• 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.

setOrder — Order flag

'sorted' (default) | 'stable'

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

Flag	Description
'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

C — Difference of A and B

vector | matrix | table | timetable

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.

ia — Index to A

column vector

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.

Extended Capabilities

Tall Arrays

Calculate with arrays that have more rows than fit in memory.

Usage notes and limitations:

• The 'stable' and 'legacy' options are not supported.

• Inputs of type 'char' are not supported.

For more information, see Tall Arrays.

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• Code generation does not support cell arrays for the first or second arguments.

• When you do not specify the 'rows' option:

  • Inputs A and B must be vectors. If you specify the 'legacy' option, then inputs A and B must be row vectors.

  • The first dimension of a variable-size row vector must have fixed length 1. The second dimension of a variable-size column vector must have fixed length 1.

  • Do not use [] to represent the empty set. Use a 1-by-0 or 0-by-1 input, for example, zeros(1,0), to represent the empty set.

  • If you specify the 'legacy' option, then empty outputs are row vectors, 1-by-0. They are never 0-by-0.

• When you specify both the 'legacy' and 'rows' options, the output ia is a column vector. If ia is empty, then it is 0-by-1. It is never 0-by-0, even if the output C is 0-by-0.

• When the setOrder is not 'stable' or when you specify the 'legacy' option, the inputs must already be sorted in ascending order. The first output, C, is sorted in ascending order.

• Complex inputs must be single or double.

• When one input is complex and the other input is real, do one of the following:

  • Set setOrder to 'stable'.

  • Sort the real input in complex ascending order (by absolute value). Suppose the real input is x. Use sort(complex(x))or sortrows(complex(x)).

• See Code Generation for Complex Data with Zero-Valued Imaginary Parts (MATLAB Coder).

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

Usage notes and limitations:

• The 'legacy' flag is not supported.

• 64-bit integers are not supported.

For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).