定义二维坐标的两个数组，作为数组索引 [英] Two arrays defining 2D coordinates, as array indices

问题描述

我有一个二维数组，称之为A.我还有另外两个二维数组，分别称为 ix 和 iy.我想创建一个输出数组，其元素是 ix 和 iy 提供的索引对处的 A 元素.我可以用如下循环来做到这一点:

I have a 2D array, call it A. I have two other 2D arrays, call them ix and iy. I would like to create an output array whose elements are the elements of A at the index pairs provided by ix and iy. I can do this with a loop as follows:

for i=1:nx
    for j=1:ny
        output(i,j) = A(ix(i,j),iy(i,j));
    end
end

如何在没有循环的情况下执行此操作?如果我执行 output = A(ix,iy)，我会在 (ix)X(iy) 的整个范围内得到 A 的值.

How can I do this without the loop? If I do output = A(ix,iy), I get the value of A over the whole range of (ix)X(iy).

推荐答案

一种更快的方法是直接使用线性索引，而无需调用 SUB2IND:

A faster way is to use linear indexing directly without calling SUB2IND:

output = A( size(A,1)*(iy-1) + ix )

...将矩阵 A 视为一维数组(按列顺序)

... think of the matrix A as a 1D array (column-wise order)

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