subsref
Subscripted reference
Syntax
Description
For classes authored in R2021b and later, the recommended process for
customizing indexing is to inherit from some combination of matlab.mixin.indexing.RedefinesParen
, matlab.mixin.indexing.RedefinesDot
, and matlab.mixin.indexing.RedefinesBrace
. For more information, see Customize Object Indexing.
Examples
Parentheses Indexing
This example shows how MATLAB® calls subsref
for the following indexing expression.
A = magic(5); A(1:2,:)
ans = 2×5
17 24 1 8 15
23 5 7 14 16
The syntax, A(1:2,:)
, results in a call to B = subsref(A,S)
where S
is a 1-by-1 structure where S.type
is '()'
and S.subs
is {1:2,':'}
. The colon character indicates a colon used as a subscript.
Brace Indexing
This example shows how MATLAB® calls subsref
for indexing expression that use braces.
C = {"one", 2, 'three'}; C{1:2}
ans = "one"
ans = 2
The syntax, C{1:2}, results in a call to [c1,c2] = subsref(C,S)
where S.type
is '{}'
and S.subs
is {[1 2]}
.
Dot Indexing
This example shows how MATLAB® calls subsref
for indexing expression that use dot notation.
A = struct('number',10);
A.number
ans = 10
The syntax A.number
results in a call to B = subsref(A,S)
where S.Type
is '.'
and S.subs
is 'number'
.
Input Arguments
A
— Indexed object array
any object
Indexed object array, passed by MATLAB as the object array that is part of the indexing expression.
S
— Indexing structure
specialized indexing structure
Indexing structure, passed by MATLAB as the indexing substruct
for the indexing expression that caused the call to subsref. This structure has these fields:
type
– Character vector or string scalar containing()
,{}
, or.
, specifying the subscript type.subs
– Cell array, character vector, or string scalar containing the actual subscripts.
Index expressions can use more than one level to form more complicated expressions. For example A{1}.field(3:5)
has three levels of indexing. For this expression, S
is a 3-by-1 structure array with these fields:
disp(S(1)) type: '{}' subs: {[1]} disp(S(2)) type: '.' subs: 'field' disp(S(3)) type: '()' subs: {[3 4 5]}
Data Types: struct
Output Arguments
B
— Result of indexing expression
any type of value
Result of indexing expression.
More About
Understanding Indexing Expressions
A(I)
is an array formed from the elements of A
specified by the subscript vector I
. The resulting array is the same size as I
except for the special case where A
and I
are both vectors. In this case, A(I)
has the same number of elements as I
but has the orientation of A
.
A(I,J)
is an array formed from the elements of the rectangular submatrix of A
, specified by the subscript vectors I
and J
. The resulting array has length(I)
rows and length(J)
columns. A colon used as a subscript indicates all elements in that dimension. For example, A(I,:)
means all columns of those rows specified by vector I
. Similarly, A(:,J)
means all rows of columns specified by J
.
A(I,J,K,...)
is the array specified by the subscripts. The result is length(I)
-by-length(J)
-by-length(K)...
.
A{I}
where A
is a cell array and I
is a scalar forms a copy of the array in the specified cell of A
. If I
has more than one element, this expression is a comma-separated list. You can also use multiple subscripts that specify a scalar element, as in A{3,4}
.
A(I).field
when A
is a structure array and I
is a scalar forms a copy of the array in the field with the name field
. If I
has more than one element, this expression is a comma-separated list. If A
is a 1-by-1 structure array, then the subscript can be dropped. In this case, A.field
is the same as A(1).field
.
Extended Capabilities
Tall Arrays
Calculate with arrays that have more rows than fit in memory.
Tall arrays support a limited subset of indexing operations. For details, see Index and View Tall Array Elements.
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™.
The subsref
function
supports GPU array input with these usage notes and limitations:
Curly brace indexing for cell arrays and dot indexing for structures are not supported (GPU arrays do not support cell arrays or structures).
Sparse GPU arrays only support referencing whole rows or columns by index. For example, you can access the fifth row of sparse matrix
A
by callingA(5,:)
orA(5,1:end)
.
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™.
Usage notes and limitations:
Curly brace indexing for cell arrays and dot indexing for structures are not supported.
For more information, see Run MATLAB Functions with Distributed Arrays (Parallel Computing Toolbox).
Version History
Introduced before R2006a
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:
How to Get Best Site Performance
Select the China site (in Chinese or English) for best site performance. Other MathWorks country sites are not optimized for visits from your location.
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
- United Kingdom (English)