清空筛选条件
清空筛选条件

how to use bsxfun or arrayfun to build the following matrix

2 次查看（过去 30 天）
Jason
Jason 2016-2-25
编辑： Walter Roberson 2016-2-25
Hi, there.
I want to use bsxfun or arrayfun to replace the following for loop.
for s=1:S
New_P(s,:)=P(s,:,U0(s));
end;
for example,
if P(：,：,1)=[1,2;3,4];
P(:,:,2)=[5,6;7,8];
U0=[1;2];
then the final result is New_P=[1,2;7,8];
Thank you in advance!
  2 个评论
Adam
Adam 2016-2-25
Is there any particular reason why you want to use arrayfun or bsxfun? arrayfun is generally slower than a for loop and is also more suited to 1d arrays than multidimensional arrays. It can certainly be used for multidimensional arrays, but it effectively just interprets it as a 1d array anyway using linear indexing on the array.
I'm not aware of a syntax of bsxfun that would be useful for this, though maybe it is. I use it for certain specific tasks so haven't used all its capabilities.
Jason
Jason 2016-2-25
thank you for your comments. because when the size of the matrix is very large, the for loop is generally very unefficiency, so i want use a vectorized expression.

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Guillaume
Guillaume 2016-2-25
Neither arrayfun nor bsxfun are useful for this. sub2ind is:
P = cat(3, [1 2;3 4], [5 6;7 8]);
U0 = [1;2];
New_P = P(sub2ind(size(P), ...
repmat((1:size(P, 1))', 1, size(P, 2)), ... rows where to pick the elements
repmat(1:size(P, 2), size(P, 1), 1), ... columns where to pick the elements
repmat(U0, 1, size(P, 2)))) %pages where to pick the elements
  1 个评论
Guillaume
Guillaume 2016-2-25
Note that you could generate the rows and columns matrix with ngrid if you prefer:
[rows, cols] = ndgrid(1:size(P, 1), 1:size(P, 2));
new_P = P(sub2ind(size(P), rows, cols, repmat(U0, 1, size(P, 2))))

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Creating and Concatenating Matrices 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by