在数组上应用一个函数，该函数以矢量化方式返回不同大小的输出 [英] Applying a function on array that returns outputs with different size in a vectorized manner

问题描述

如何应用使用arrayfun将非标量输出返回到数组的函数?

How to apply a function that returns non scalar output to arrays using arrayfun?

例如-如何将以下代码向量化?

For example - How to vectorize the following code?

array = magic(5);
A = cell(size(array));
for i=1:5
    for j=1:5
      A{i,j} = 1:array(i,j);
    end
end

这种天真的矢量化尝试不起作用，因为输出不是标量

This naive attempt to vectorize does not work, because the output is not a scalar

array = magic(5);
result = arrayfun(@(x)(1:x),array);

推荐答案

有2种方法可以实现:

可以将"UniformOutput"设置为false.然后，结果是一个单元格数组.

It is possible to set 'UniformOutput' to false. Then, the result is a cell array.

   result = arrayfun(@(x)(1:x),array,'UniformOutput',false);

但是我今天发现了一个不错的技巧，该函数本身可以返回一个单元格.这样就无需每次都键入'UniformOutput',false.

But there is a nice trick that I have found today, the function itself can return a cell. This removes the need of typing 'UniformOutput',false each and every time.

    result = arrayfun(@(x){1:x},array)

什么是真正有趣的，在这里我不必键入@(X)({1:x})，但只能使用花括号@(X){1:x}

What is really interesting here that I don't have to type @(X)({1:x}) but I can define it only by using curly bracers @(X){1:x}

编辑(1):正如@Jonas正确指出的那样，毫无疑问不需要常规护腕()，因为它们是可选的.例如，@(x) x+1是有效的语法.

Edit(1): As @Jonas correctly points out, there is no wonder that the regular bracers () are not needed, as they are optional. For example, @(x) x+1 is a valid syntax.

编辑(2):使用花括号方法或UniformOutput,false之间有很小的区别.当输入数组为空时，它们的行为是不同的.

Edit(2): There is a small difference between using the curly bracers method or the UniformOutput,false. When the input array is empty, their behavior is different.

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