与Matlab中的R rep类似的功能 [英] A similar function to R's rep in Matlab

问题描述

我正在寻找一个功能与Matlab R中的rep函数类似的函数.例如，使用rep，我可以执行以下操作:

> rep(c(1,2,3),times=3)
[1] 1 2 3 1 2 3 1 2 3

> rep(c(1,2,3),each=3)
[1] 1 1 1 2 2 2 3 3 3
> 

在matlab中，有repmat函数完成了第一部分

>> repmat([1,2,3],1,3)

ans =

     1     2     3     1     2     3     1     2     3

但不是第二部分(或者至少我不知道该怎么做).

有什么建议吗?

解决方案

您可以通过首先定义如下函数来相当接近地重现R中rep函数的语法:

function [result]=rep(array, count)
matrix = repmat(array, count,1);
result = matrix(:);

然后，您可以通过使用行向量或列向量进行调用来重现所需的行为:

>> rep([1 2 3],3)
ans =
 1     1     1     2     2     2     3     3     3

>> rep([1 2 3]',3)
ans =
 1     2     3     1     2     3     1     2     3

请注意，我在第二次调用中使用了transpose(')运算符将输入数组作为列向量(3x1矩阵)传递.

我在笔记本电脑上对此进行了基准测试，对于具有100,000个元素重复100次的基本阵列，它比使用上面的ceil选项快2到8倍，具体取决于您要使用第一种还是第二种排列方式. /p>

I am looking for a function that behaves similarly to the rep function in R for Matlab. For example with rep I can do the following:

> rep(c(1,2,3),times=3)
[1] 1 2 3 1 2 3 1 2 3

> rep(c(1,2,3),each=3)
[1] 1 1 1 2 2 2 3 3 3
> 

In matlab there is the repmat function which accomplishes the first part

>> repmat([1,2,3],1,3)

ans =

     1     2     3     1     2     3     1     2     3

but not the second part (or at least I can't figure out how to do it).

Any suggestions?

解决方案

You can reproduce the syntax of the rep function in R fairly closely by first defining a function as follows:

function [result]=rep(array, count)
matrix = repmat(array, count,1);
result = matrix(:);

Then you can reproduce the desired behavior by calling with either a row or column vector:

>> rep([1 2 3],3)
ans =
 1     1     1     2     2     2     3     3     3

>> rep([1 2 3]',3)
ans =
 1     2     3     1     2     3     1     2     3

Note I have used the transpose (') operator in the second call to pass the input array as a column vector (a 3x1 matrix).

I benchmarked this on my laptop, and for a base array with 100,000 elements repeated 100 times, it was between 2 to 8 times faster than using the ceil option above, depending on whether you want the first or the second arrangement.

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