Unique values in array
collapse all in page
Syntax
C = unique(A)
C = unique(A,setOrder)
C = unique(A,occurrence)
C = unique(A,___,'rows')
C = unique(A,'rows',___)
[C,ia,ic] = unique(___)
[C,ia,ic]= unique(A,'legacy')
[C,ia,ic]= unique(A,'rows','legacy')
[C,ia,ic]= unique(A,occurrence,'legacy')
[C,ia,ic]= unique(A,'rows',occurrence,'legacy')
Description
example
C = unique(A)
returns the same data as in A
, but with no repetitions. C
is in sorted order.
If
A
is a table or timetable, thenunique
returns the unique rows inA
in sorted order. For timetables,unique
takes row times and row values into account when determining whether rows are unique, and sorts the output timetableC
by row times.If
A
is a categorical array, then the sort order is determined by the order of the categories.
example
C = unique(A,setOrder)
returns the unique values of A
in a specific order. setOrder
can be 'sorted'
(default) or 'stable'
.
C = unique(A,occurrence)
specifies which indices to return in case of repeated values. occurrence
can be 'first'
(default) or 'last'
.
example
C = unique(A,___,
and 'rows'
)
treat each row of C
= unique(A
,'rows'
,___)A
as a single entity and return the unique rows of A
in sorted order. You must specify A
and optionally can specify setOrder
or occurrence
.
The 'rows'
option does not support cell arrays.
[C,ia,ic] = unique(___)
also returns index vectors ia
and ic
using any of the previous syntaxes.
If A is a vector, then
C = A(ia)
andA = C(ic)
.If
A
is a matrix or array, thenC = A(ia)
andA(:) = C(ic)
.If the
'rows'
option is specified, thenC = A(ia,:)
andA = C(ic,:)
.If
A
is a table or a timetable, thenC = A(ia,:)
andA = C(ic,:)
.
example
[C,ia,ic]= unique(A,'legacy')
, [
, C
,ia
,ic
]= unique(A
,'rows','legacy')[
,and C
,ia
,ic
]= unique(A
,occurrence,'legacy')[
preserve the behavior of the C
,ia
,ic
]= unique(A
,'rows',occurrence
,'legacy')unique
function from R2012b and prior releases.
The 'legacy'
option does not support categorical arrays, datetime arrays, duration arrays, calendarDuration arrays, tables, or timetables.
Examples
collapse all
Unique Values in Vector
Open Live Script
Define a vector with a repeated value.
A = [9 2 9 5];
Find the unique values of A
.
C = unique(A)
C = 1×3 2 5 9
Unique Rows in Table
Open Live Script
Create a table with some repeated data.
Name = {'Fred';'Betty';'Bob';'George';'Jane'};Age = [38;43;38;40;38];Height = [71;69;64;67;64];Weight = [176;163;131;185;131];A = table(Age,Height,Weight,'RowNames',Name)
A=5×3 table Age Height Weight ___ ______ ______ Fred 38 71 176 Betty 43 69 163 Bob 38 64 131 George 40 67 185 Jane 38 64 131
Find the unique rows of A
. unique
returns the rows of A
in sorted order by the first variable Age
and then by the second variable Height
.
C = unique(A)
C=4×3 table Age Height Weight ___ ______ ______ Bob 38 64 131 Fred 38 71 176 George 40 67 185 Betty 43 69 163
Find the table rows with unique values in the first variable Age
. If you only want one table variable to contain unique values, you can use the indices returned by unique
to extract those rows from the table.
[C,ia] = unique(A.Age);B = A(ia,:)
B=3×3 table Age Height Weight ___ ______ ______ Fred 38 71 176 George 40 67 185 Betty 43 69 163
Unique Values and Their Indices
Open Live Script
Define a vector with a repeated value.
A = [9 2 9 5];
Find the unique values of A
and the index vectors ia
and ic
, such that C = A(ia)
and A = C(ic)
.
[C, ia, ic] = unique(A)
C = 1×3 2 5 9
ia = 3×1 2 4 1
ic = 4×1 3 1 3 2
Unique Rows in Matrix
Open Live Script
Create a 10-by-3 matrix with some repeated rows.
A = randi(3,10,3)
A = 10×3 3 1 2 3 3 1 1 3 3 3 2 3 2 3 3 1 1 3 1 2 3 2 3 2 3 3 2 3 3 1
Find the unique rows of A
based on the data in the first two columns. Specify three outputs to return the index vectors ia
and ic
.
[C,ia,ic] = unique(A(:,1:2),'rows')
C = 7×2 1 1 1 2 1 3 2 3 3 1 3 2 3 3
ia = 7×1 6 7 3 5 1 4 2
ic = 10×1 5 7 3 6 4 1 2 4 7 7
Use ia
to index into A
and retrieve the rows that have unique combinations of elements in the first two columns.
uA = A(ia,:)
uA = 7×3 1 1 3 1 2 3 1 3 3 2 3 3 3 1 2 3 2 3 3 3 1
Count of Unique Elements
Open Live Script
Find the unique elements in a vector and then use accumarray
to count the number of times each unique element appears.
Create a vector of random integers from 1 through 5.
a = randi([1 5],200,1);
Find the unique elements in the vector. Return the index vectors ia
and ic
.
[C,ia,ic] = unique(a);
Count the number of times each element in C
appears in a
. Specify ic
as the first input to accumarray
and 1
as the second input so that the function counts repeated subscripts in ic
. Summarize the results.
a_counts = accumarray(ic,1);value_counts = [C, a_counts]
value_counts = 5×2 1 46 2 36 3 38 4 39 5 41
Unique Values in Vector with Specified Order
Open Live Script
Use the setOrder
argument to specify the ordering of the values in C
.
Specify 'stable'
if you want the values in C
to have the same order as in A
.
A = [9 2 9 5];[C, ia, ic] = unique(A,'stable')
C = 1×3 9 2 5
ia = 3×1 1 2 4
ic = 4×1 1 2 1 3
Alternatively, you can specify 'sorted'
order.
[C, ia, ic] = unique(A,'sorted')
C = 1×3 2 5 9
ia = 3×1 2 4 1
ic = 4×1 3 1 3 2
Unique Values in Array Containing NaNs
Open Live Script
Define a vector containing NaN
.
A = [5 5 NaN NaN];
Find the unique values of A
.
C = unique(A)
C = 1×3 5 NaN NaN
unique
treats NaN
values as distinct.
Unique Elements in Presence of Numerical Error
Open Live Script
Create a vector x
. Obtain a second vector y
by transforming and untransforming x
. This transformation introduces round-off differences in y
.
x = (1:6)'*pi;y = 10.^log10(x);
Verify that x
and y
are not identical by taking the difference.
x-y
ans = 6×110-14 × 0.0444 0 0 0 0 -0.3553
Use unique
to find the unique elements in the concatenated vector [x;y]
. The unique
function performs exact comparisons and determines that some values in x
are not exactly equal to values in y
. These are the same elements that have a nonzero difference in x-y
. Thus, c
contains values that appear to be duplicates.
c = unique([x;y])
c = 8×1 3.1416 3.1416 6.2832 9.4248 12.5664 15.7080 18.8496 18.8496
Use uniquetol
to perform the comparison using a small tolerance. uniquetol
treats elements that are within tolerance as equal.
C = uniquetol([x;y])
C = 6×1 3.1416 6.2832 9.4248 12.5664 15.7080 18.8496
Unique Entries in Cell Array of Character Vectors
Open Live Script
Create a cell array of character vectors.
A = {'one','two','twenty-two','One','two'};
Find the unique character vectors contained in A
.
C = unique(A)
C = 1x4 cell {'One'} {'one'} {'twenty-two'} {'two'}
Cell Array of Character Vectors with Trailing White Space
Open Live Script
Create a cell array of character vectors, A
, where some of the vectors have trailing white space.
A = {'dog','cat','fish','horse','dog ','fish '};
Find the unique character vectors contained in A
.
C = unique(A)
C = 1x6 cell {'cat'} {'dog'} {'dog '} {'fish'} {'fish '} {'horse'}
unique
treats trailing white space in cell arrays of character vectors as distinct characters.
Preserve Legacy Behavior of unique
Open Live Script
Use the 'legacy'
flag to preserve the behavior of unique
from R2012b and prior releases in your code.
Find the unique elements of A
with the current behavior.
A = [9 2 9 5];[C1, ia1, ic1] = unique(A)
C1 = 1×3 2 5 9
ia1 = 3×1 2 4 1
ic1 = 4×1 3 1 3 2
Find the unique elements of A
, and preserve the legacy behavior.
[C2, ia2, ic2] = unique(A, 'legacy')
C2 = 1×3 2 5 9
ia2 = 1×3 2 4 3
ic2 = 1×4 3 1 3 2
Input Arguments
collapse all
A
— Input array
array
Input array.
If
A
is a table, thenunique
does not take row names into account. Two rows that have the same values, but different names, are considered equal.If
A
is a timetable, thenunique
takes row times into account. Two rows that have the same values, but different times, are not considered equal.If
A
is a categorical array, then the sort order is determined by the order of the categories. To see the sort order of a categorical array, use the categories function.
A
can also be an object with the following class methods:
sort
(orsortrows
for the'rows'
option)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
can be an array 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 |
---|---|
| The values (or rows) in Example C = unique([5 5 3 4],'sorted') C = 3 4 5 |
| The values (or rows) in Example C = unique([5 5 3 4],'stable') C = 5 3 4 |
Data Types: char
| string
occurrence
— Occurrence flag
'first'
(default) | 'last'
Occurrence flag, specified as 'first'
or 'last'
, indicates whether ia should contain the first or last indices to repeated values found in A.
Occurrence Flag | Meaning |
---|---|
'last' | If there are repeated values (or rows) in A , then ia contains the index to the last occurrence of the repeated value. For example: [C,ia,ic] = unique([9 9 9],'last','legacy') returns ia = 3 . This is the default behavior when the 'legacy' flag is specified. |
'first' | If there are repeated values (or rows) in A , then ia contains the index to the first occurrence of the repeated value. For example: [C,ia,ic] = unique([9 9 9],'first') returns ia = 1 . This is the default behavior. |
Data Types: char
| string
Output Arguments
collapse all
C
— Unique data of A
array
Unique data of A, returned as an array. The class of C
is the same as the class of the input A
. The shape of C
depends on whether the input is a vector or a matrix:
If the
'rows'
flag is not specified andA
is a row vector, thenC
is a row vector.If the
'rows'
flag is not specified andA
is not a row vector, thenC
is a column vector.If the
'rows'
flag is specified, thenC
is a matrix containing the unique rows ofA
.
ia
— Index to A
column vector
Index to A, returned as a column vector of indices to the first occurrence of repeated elements. When the 'legacy'
flag is specified, ia
is a row vector that contains indices to the last occurrence of repeated elements.
The indices generally satisfy C = A(ia)
. If A
is a table, or if the 'rows'
option is specified, then C = A(ia,:)
.
ic
— Index to C
column vector
Index to C, returned as a column vector when the 'legacy'
flag is not specified. ic
contains indices that satisfy the following properties.
If
A
is a vector, thenA = C(ic)
.If
A
is a matrix or array, thenA(:) = C(ic)
.If
A
is a table, or if the'rows'
option is specified, thenA = C(ic,:)
.
Tips
Use
uniquetol
to find unique floating-point numbers using a tolerance.To find unique rows in tables or timetables with respect to a subset of variables, you can use column subscripting. For example, you can use
unique(A(:,
, wherevars
))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.
This function supports tall arrays with the limitations:
For tall vectors and tall tables, use the syntaxes:
C = unique(A)
[C,ia,ic] = unique(A)
For tall matrices, use the syntaxes:
C = unique(A,'rows')
[C,ia,ic] = unique(A,'rows')
For more information, see Tall Arrays for Out-of-Memory Data.
C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.
Usage notes and limitations:
When you do not specify the
'rows'
option:The input
A
must be a vector. If you specify the'legacy'
option, the inputA
must be a row vector.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.
The input
[]
is not supported. 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
'rows'
option and the'legacy'
option, outputsia
andic
are column vectors. If these outputs are empty, then they are 0-by-1, even if the outputC
is 0-by-0.When the
setOrder
is not'stable'
or when you specify the'legacy'
option, the inputA
must already be sorted in ascending order. The first output,C
, is sorted in ascending order.Complex inputs must be
single
ordouble
.
Thread-Based Environment
Run code in the background using MATLAB® backgroundPool
or accelerate code with Parallel Computing Toolbox™ ThreadPool
.
This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.
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).
Distributed Arrays
Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.
This function fully supports distributed arrays. For more information, see Run MATLAB Functions with Distributed Arrays (Parallel Computing Toolbox).
Version History
Introduced before R2006a
See Also
union | intersect | ismember | issorted | setdiff | setxor | sort | uniquetol
MATLAB Command
You clicked a link that corresponds to this MATLAB command:
Run the command by entering it in the MATLAB Command Window. Web browsers do not support MATLAB commands.
Select a Web Site
Choose a web site to get translated content where available and see local events and offers. Based on your location, we recommend that you select: .
You can also select a web site from the following list:
Americas
- América Latina (Español)
- Canada (English)
- United States (English)
Europe
- Belgium (English)
- Denmark (English)
- Deutschland (Deutsch)
- España (Español)
- Finland (English)
- France (Français)
- Ireland (English)
- Italia (Italiano)
- Luxembourg (English)
- Netherlands (English)
- Norway (English)
- Österreich (Deutsch)
- Portugal (English)
- Sweden (English)
- Switzerland
- Deutsch
- English
- Français
- United Kingdom (English)
Contact your local office