如何在MATLAB中初始化结构数组? [英] How to initialize an array of structs in MATLAB?

问题描述

如何在MATLAB中预分配结构数组?我想在此示例中预分配"a"，以使其不会多次调整大小.

How can I preallocate an array of structs in MATLAB? I want to preallocate "a" in this example so that it does not resize several times.

a = []
for i = 1:100
  a(i).x = i;
end

推荐答案

使用repmat是迄今为止最有效的预分配结构的方法:

Using repmat is by far the most efficient way to preallocate structs :

N = 10000;    
b = repmat(struct('x',1), N, 1 );

与使用索引进行预分配相比，使用Matlab 2011a的速度要快〜10倍，如

This is ~10x faster using Matlab 2011a than preallocating via indexing, as in

N      = 10000;
b(N).x = 1

索引方法仅比不预先分配要快.

The indexing method is only marginally faster than not preallocating.

No preallocation:            0.075524    
Preallocate Using indexing:  0.063774
Preallocate with repmat:     0.005234

---

---

下面的代码，以备您验证.

---

---

Code below in case you want to verify.

        clear;
        N = 10000;

    %1) GROWING A STRUCT
        tic;
        for ii=1:N
            a(ii).x(1)=1;    
        end
        noPreAll = toc;        

    %2)PREALLOCATING A STRUCT
        tic;
        b = repmat( struct( 'x', 1 ), N, 1 );
        for ii=1:N
            b(ii).x(1)=1;    
        end;  
        repmatBased=toc;        

    %3)Index to preallocate
        tic;
        c(N).x = 1;
        for ii=1:N
            c(ii).x(1)=1;    
        end;  
        preIndex=toc;

        disp(['No preallocation:        ' num2str(noPreAll)])            
        disp(['Preallocate Indexing:    ' num2str(preIndex)])
        disp(['Preallocate with repmat: ' num2str(repmatBased)])

命令窗口中的结果:

No preallocation:        0.075524    
Preallocate Indexing:    0.063774
Preallocate with repmat: 0.0052338
>> 

PS .我想知道为什么这是真的，如果有人能解释的话.

P.S. I'd be interested to know why this is true, if anyone can explain it.

这篇关于如何在MATLAB中初始化结构数组?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！