subsref

Subscripted reference

Classes overload subsref to implement custom indexing behavior for objects of the class. For more information, see Object Indexing.

Syntax

B = subsref(A,S)

Description

example

B = subsref(A,S) is called by MATLAB® for the syntax A(i), A{i}, or A.i when A is an object.

Examples

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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.

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]}.

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

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Indexed object array, passed by MATLAB as the object array that is part of the indexing expression.

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

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Result of indexing expression.

More About

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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

Introduced before R2006a