# 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 calling`A(5,:)`

or`A(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**

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