substruct

Create indexing structure argument

Syntax

S = substruct(type,subs)

S = substruct(type1,subs1,type2,subs2,...)

Description

S = substruct(type,subs) creates a structure with the information required by the subsref and subsasgn functions. The type argument indicates whether the indexing expression is parentheses, dot, or brace. The corresponding subs argument is a field name for dot indexing or a cell array containing index vectors for parentheses or brace indexing.

Note

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

S = substruct(type1,subs1,type2,subs2,...) creates a structure array for a compound indexing expression, with each type and subs pair representing one indexing expression.

Examples

Substruct with One Level of Indexing

Create a 2-by-2 array and display the element at (1,2) using the standard indexing syntax.

A = magic(2);
A(1,2)

ans =

     3

Use the substruct function to create a structure that describes the indexing operation.

S = substruct("()",{1,2})

S = 

  struct with fields:

    type: "()"
    subs: {[1]  [2]}

Call subsref with the result from substruct to perform the operation equivalent to A(1,2).

subsref(A,S)

ans =

     3

Substruct with Compound Indexing

Create a 1-by-2 structure array x with fields name and numbers. Display the data numbers(3:4) of the entry at x(2).

x.name = "Clara";
x.numbers = [1 3 5 7];
x(2).name = "Jorge";
x(2).numbers = [2 4 6 8];
x(2).numbers(3:4)

ans =

     6     8

x(2).numbers(3:4) has three indexing expressions: a parentheses, a dot, and a second parentheses expression. Use the substruct function to create a structure array that describes the indexing expression.

 S = substruct("()",{2},".","numbers","()",{3:4});

Call subsref using the result from substruct to perform the operation equivalent to x(2).numbers(3:4).

subsref(x,S)

ans =

     6     8

Input Arguments

type — Type of indexing expression

"()""." | "{}"

Type of indexing expression, specified as "()", ".", or "{}" to indicate parentheses, dot, or brace indexing, respectively. The value can be a character vector or string scalar.

subs — Subscript values

character vector | string scalar | cell array of vectors

Subscript values, specified as a character vector or string scalar for dot indexing or a cell array of index vectors for parentheses or brace indexing.

Output Arguments

S — Indexing argument structure

structure array

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

• type — Type of indexing expression, 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]}

Tips

• You can overload subsref and subsasgn 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, see Customize Object Indexing.

Extended Capabilities

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.

Version History

Introduced before R2006a