在Matlab中有与R的负索引等效吗? [英] Is there an equivalent to R's negative indexing in Matlab?

问题描述

在R中，如果我们有一个向量和一个索引列表，则可以使用负索引来表达我们想要除这些索引之外的所有元素"的想法.特别是，请考虑以下R代码:

In R, if we have a vector and a list of indices, we can express the idea that we want "all elements except these indices" using a negative index. In particular, consider the following R code:

data = rnorm(100)
indices = sample(1:length(data), length(data)/2)
training_data = data[indices]
test_data = data[-indices]

此代码之后，sampled_data包含data中所有元素的索引未包含在indices中. 在matlab中是否与此等效?

After this code, sampled_data contains all the elements in data whose indices are not included in indices. Is there an equivalent to this in matlab?

我直接尝试使用相同的语法(当然是()而不是[]，但这只是给出了错误

I tried directly using the same syntax (of course wtih () instead of [], but it just gave the error

Subscript indices must either be real positive integers or logicals.

推荐答案

Matlab不允许使用负索引.您可以删除元素的方法是:

Matlab does not allow negative indices. What you can do to remove elements is this:

data2 = data;
data2(indices) = [];  % remove selected elements

但是在进行机器学习时，我更喜欢使用逻辑索引:

But when doing machine-learning stuff I prefer to use logical indexing:

istest = randn(length(data), 1) < 0;   % random logicals: 50% 0's and 50% 1's
istrain = ~istest;
% Now operate on data(istest) and data(istrain).

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