避免在MATLAB中嵌套for循环 [英] avoiding nested for loops in MATLAB

问题描述

我在MATLAB中有一种情况，我想为某些参数值评估函数.从任意数量的数组中提取参数，并且每个数组可以具有任意数量的元素.在调用函数之前，我知道数组的数量和其中的元素数量.

I have a scenario in MATLAB where I would like to evaluate a function for certain parameter values. The parameters are extracted from an arbitrary number of arrays, and each array can have an arbitrary number of elements. I know the number of arrays and the number of elements in them before I call the function.

例如，假设我有数组A = [a1 a2 ... aL]，B = [b1 b2 ... bM]和C = [c1 c2 ... cN].

For example, say I have arrays A = [a1 a2 ... aL], B = [b1 b2 ... bM] and C = [c1 c2 ... cN].

for i = 1:length(A)
    for j = 1:length(B)
        for k = 1:length(C)
            myfunc(A(i), B(j), C(k))
        end
     end
end

我正在考虑采用A的L元素，B的M元素和C的N元素，并将它们展平为单元格数组，并使用单个for循环进行迭代在这个细胞阵列上.

I am considering taking the L elements of A, M elements of B and N elements of C, and flatenning them into a cell array, and iterating with a single for loop over this cell array.

我想知道是否有一个MATLAB函数可以执行以下操作……结果不必一定是单元格数组.我想要一种避免多个嵌套的for循环的方法.少数循环是可以的，但是随着循环次数的增加，读取和维护它非常困难.

I was wondering if there was a MATLAB function that does something like this ... The result does not have to be a cell array. I want a way to avoid having multiple nested for loops. It is fine for a small number of loops, but as this number grows, it is pretty difficult to read and maintain.

推荐答案

可用于将多个嵌套循环展平为一个.它生成值的所有组合(下面的代码中的变量aa，bb，cc)，因此可以使用单个索引(下面的k)遍历所有组合.但是请注意，生成所有组合可能需要大量内存，具体取决于您的L，M，N.

ndgrid can be used to flatten several nested loops into one. It generates all combinations of values (variables aa, bb, cc in the code below), so that a single index (k below) can be used to traverse all combinations. But note that generating all combinations may required a lot of memory, depending on your L, M, N.

[cc, bb, aa] = ndgrid(C, B, A); %// outermost variable should be rightmost here
for k = 1:numel(aa)
     myfunc(aa(k), bb(k), cc(k));
end

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