MATLAB:定期提取元素 [英] MATLAB: Extracting elements periodically

问题描述

我想使用:运算符从向量中提取元素，但要定期进行.例如，说a={1,2,3, ..., 10}，我想在步骤2中提取元素，更改引用.那我想得到

I'd like to extract elements from a vector using the :-operator, but periodically. As an example, say a={1,2,3, ..., 10} and that I would like to extract elements in steps of 2, changing the reference. Then I would like to get

ref 1: 1 3 5 7 9
ref 2: 2 4 6 8 10
ref 3: 3 5 7 9 1
...

MATLAB中是否有关键字强制其为周期性的?还是我必须先将circshift应用于数组，然后提取?

Is there a keyword in MATLAB to force it to be periodic? Or do I have to apply circshift to the array first, and then extract?

推荐答案

您可以使用模运算:mod(...-1, numel(a))+1来构建索引.那些-1和+1是必需的，因此生成的索引从1开始(而不是从0开始).

You can build the index using a modulo operation: mod(...-1, numel(a))+1. Those -1 and +1 are needed so the resulting index is 1-based (not 0-based).

a = [1 2 3 4 5 6 7 8 9 10]; % vector to be indexed
ref = 3; % first value for index
step = 2; % step for index
ind = mod(ref+(0:step:numel(a)-1)-1,numel(a))+1; % build index
result = a(ind); % apply index

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