matrix indexing and creating a new matrix with new size

2012 6 6
4 个回答
回答已采纳
2 次查看（30 天）

0 个投票

Dear experts, I hope somebody can help me. I have a n*4 matrix. In a loop I want to index some rows (the range is not fixed) from column 1 and put them in a new matrix with separate columns. I guess since the size of rows are not the same, Matlab gives me the mismatch dimension error for new matrix! Any solution? Thanks in advance Sobhan

请先登录，再回答此问题。

 采纳的回答

Wayne King
Wayne King 2012-6-6

0 个投票

How about
clear output
For f = 1:nfiles
IndexStart= RHs(RHs<peak);
IndexEnd= RHs(RHs>peak);
output{f} = Mydata (Index1:Index2,1);
end
If you know how big output is going to be in advance you can preallocate the cell array.

1 个评论
显示 -1更早的评论 隐藏 -1更早的评论

Sobhan
Sobhan 2012-6-6
thanks Wayne,
your solution only gives me a cell array with the size of output and not a matrix.
Cheers

请先登录，再进行评论。

更多回答（3 个）

Wayne King
Wayne King 2012-6-6

0 个投票

How about using a cell array? Beyond that I think you will need to give us a little MATLAB example to illustrate your issue.

1 个评论
显示 -1更早的评论 隐藏 -1更早的评论

Sobhan
Sobhan 2012-6-6
Hi Wayne,
This is a simplified version of my loop.
For f = 1:nfiles
IndexStart= RHs(RHs<peak);
IndexEnd= RHs(RHs>peak);
output (:, f) = Mydata (Index1:Index2,1);
End
only the first file can be saved in output but it gives error for the second file because it has different rows. Is it clear now? Sorry I am really new to matlab.
Cheers
Sobahn

请先登录，再进行评论。

Christoph
Christoph 2012-6-6

0 个投票

Hi Sobhan,
as Wayne said, an example might be helpful. Nevertheless you might use:
X_new(:,end+1) = [X_old(:,i); zeros(size(X_new, 1) - size(X_old, 1),1)];
in your loop as long as the length of the old matrix is shorter or equal as the length of the new one. But waynes answer is the "politcally correct" one.

2 个评论
显示 无 隐藏 无

Sobhan
Sobhan 2012-6-6
Hi,
Thanks for the answer. I gave an example above.
The length of the new matrix is sometimes bigger sometimes smaller. I think I need something to add a new column with the size of new file to previously created matrix. I am trying to figure it out.
Cheers
Christoph
Christoph 2012-6-6
ok, try to implement the next few nasty codelines:
if length(X_new) < length(X_old)
X_new(end+1,:) = zeros(length(X_old)-length(X_new), size(X_new, 2))
end

请先登录，再进行评论。

Sobhan
Sobhan 2012-6-8

0 个投票

Cell array was the solution: output{f} = Mydata (Index1:Index2,1)

类别

在 帮助中心 和 File Exchange 中查找有关 Matrix Indexing 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