MATLAB 中是否有该表达式的非迭代等价形式？

发布于 2024-10-20 20:11:11 字数 107 浏览 3 评论 0原文

表达式为：

for i=1:n
    X(:,i) = [P{i}(:)];
end

其中 X 是 DxN 矩阵，P 是元胞数组。

原文

The expression is:

for i=1:n
    X(:,i) = [P{i}(:)];
end

where X is a DxN matrix and P is a cell-array.

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装纯掩盖桑 2024-10-27 20:11:11

reshape(cat(3,P{:}),[numel(P{1}) n])

当然，上面的解决方案只是为了好玩。我建议对这两种解决方案进行分析，并且仅在具有显着性能优势的情况下使用该解决方案。

可维护性和可读性也是编写代码时需要考虑的非常重要的因素。

reshape(cat(3,P{:}),[numel(P{1}) n])

Of course, the above solution is just for fun. I would recommend profiling both solutions and only using this one if it has a significant performance advantage.

Maintenance and readability are also very important factors to consider when writing code.

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你是我的挚爱i 2024-10-27 20:11:11

如果您通过 mat2cell 获取元胞数组，您可能希望将图像块排列到数组 X 的列中。这可以使用命令 IM2COL 一步完成

%# rearrange the large array so that each column of X
%# corresponds to the 4 pixels of each 2-by-2 block
X = im2col(largeArray,[2 2],'distinct');

If you obtained the cell array via mat2cell, you may be wanting to arrange blocks of an image into the columns of an array X. This can be achieved in a single step using the command IM2COL

%# rearrange the large array so that each column of X
%# corresponds to the 4 pixels of each 2-by-2 block
X = im2col(largeArray,[2 2],'distinct');

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三生一梦 2024-10-27 20:11:11

你也许可以逃脱：

P{1} = [ 1 2; 3 4];
P{2} = [ 7 8; 9 10];
P{3} = [ 11 12; 13 14];
X = [P{:}]

X =

     1     2     7     8    11    12
     3     4     9    10    13    14

然后某种 reshape() 到达你想要的地方。

You might be able to get away with:

P{1} = [ 1 2; 3 4];
P{2} = [ 7 8; 9 10];
P{3} = [ 11 12; 13 14];
X = [P{:}]

X =

     1     2     7     8    11    12
     3     4     9    10    13    14

Then some sort of reshape() to get to where you want to be.

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