subsref - Indexed reference using function call - MATLAB (original) (raw)

Indexed reference using function call

Syntax

Description

`B` = subsref([A](#mw%5F3a71901f-ffb4-40c5-b043-ce2c07a5e9c8),[S](#mw%5F35fd8668-bad0-4fe6-984e-4af513df821b)) returns the result from a parentheses, brace, or dot indexing expression, or a combination of one or more of those types, performed on the arrayA. The structure S contains the details of the indexing expression to be performed.

Note

Performing indexing by calling the subsref function explicitly is always slower than the equivalent indexing statement.

example

Examples

collapse all

Create a 5-by-5 array and display the first two rows using the standard indexing syntax.

A = magic(5); B = A(1:2,:)

B = 2×5

17    24     1     8    15
23     5     7    14    16

Call subsref to perform the same operation. Use the substruct function to create the structure that describes the indexing expression.

C = subsref(A,substruct('()',{1:2,':'}))

C = 2×5

17    24     1     8    15
23     5     7    14    16

Create a 1-by-3 cell array and display the first two elements using the standard indexing syntax.

C = {"one",2,'three'}; [c1,c2] = C{1:2}

Call subsref to perform the same operation. Use the substruct function to create the structure that describes the indexing expression.

[d1,d2] = subsref(C,substruct('{}',{1:2}))

Create a structure with one field that has a vector value. Display the second element of the vector using the standard indexing syntax.

A.data = [5 10 15]; A.data(2)

Call subsref to perform the same operation. Use the substruct function to create the structure that describes the indexing expression. The compound indexing expression includes a dot reference and a parentheses reference.

subsref(A,substruct(".","data","()",{2}))

Input Arguments

collapse all

Target of indexing expression, specified as an array of any data type.

Indexing argument structure, also referred to as the_substruct_, specified as a structure array. Each structure has two fields:

type — Type of indexing operation, specified as "()", ".", or"{}" to indicate parentheses, dot, or brace indexing, respectively. The value can be a character vector or string scalar.
subs — Subscript values, specified as a character vector or string for dot indexing or a cell array of index vectors for parentheses or brace indexing.

S is a scalar structure for single indexing expressions, like A{1}, or a structure array for compound indexing expressions. For example, A{1}.field(3:5) has three levels of indexing. For this expression, S is a 1-by-3 structure array:

S(1)	type: '{}'subs: {[1]}
S(2)	type: '.'subs: 'field'
S(3)	type: '()'subs: {[3 4 5]}

Data Types: struct

Tips

You can overload subsref andsubsasgn to customize indexing for your classes. However, for most 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, seeCustomize Object Indexing.

Extended Capabilities

expand all

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 matrixA by calling A(5,:) orA(5,1:end).

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

Version History

Introduced before R2006a