计算符合条件的值 [英] Counting values that meet a condition

问题描述

我正在尝试计算列向量中的值大于 0.5 的次数.下面的代码将我带到了我需要的位置，但我想知道这是执行此操作的最有效方法.

I am trying to count the number of times a value in a column vector is greater than 0.5. The code below gets me where I need to be but I am wondering is this the most efficient way to do this.

n = 500
AA = rand(n,1);
for i = 1:n
    if abs(AA(i))>0.5
      BB(i)=1;
    else
      BB(i)=0;
    end
end
sBB = sum(BB);
SD = sBB/n;

推荐答案

此任务可受益于向量化:

This task can benefit from vectorization:

n = 500
AA = rand(n,1); % You used vectorization already (!) and not create each entry separately...
BB = AA>0.5;    % Results in a vector of logicals which signifies where the condition was met
SD = sum(BB)/n; % Can also be `nnz(BB)/n` or `mean(BB)`

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