Converting a 2d array into a 3d array

15 次查看（过去 30 天）
Vinay Killamsetty
Vinay Killamsetty 2021-11-28
回答： Turlough Hughes 2021-11-28
Hi,
I am having a 2d array with size mxn
I want to convert each column into a seperate 2d diagonal matrix--- a total of 'n' diagonal matrices of size mxm
Then combining all the 2d diagonal matrices as a single 3d matrix.---size mxmxn
I tried to do this with employing a for-loop but it is taking lot of time
Can this be done without using a loop and at a faster speed?
  2 个评论
Turlough Hughes
Turlough Hughes 2021-11-28
Can you give an example of the code you have implemented?
Vinay Killamsetty
Vinay Killamsetty 2021-11-28
编辑：Vinay Killamsetty 2021-11-28
size of Z_int is mxn
Z = nan(m,m,n)
for i = 1 : size( Z_int , 2)
Z( : , : , i ) = diag( (Z_int( :, i ) ) ;
end

请先登录，再进行评论。

请先登录，再回答此问题。

回答（2 个）

Chunru
Chunru 2021-11-28
Ran in:
"it is taking lot of time" for what size of array?
m=200; n=100;
Z_int = rand(m, n);
Z = nan(m,m,n);
tic
for i = 1 : size( Z_int , 2)
Z( : , : , i ) = diag( Z_int( :, i ) );
end
toc
Elapsed time is 0.009776 seconds.
Turlough Hughes
Turlough Hughes 2021-11-28
You could write a linear index for the diagonal elements as follows:
[m,n] = size(Z_int)
Z = zeros(m,m,n);
idx = repmat((1:m+1:m^2).',1,n) + m^2*(0:n-1);
Z(idx(:)) = Z_int(:)
This is 2-4x faster for m >= 400 on my computer (n=500), however, on the matlab servers its a slightly slower. Whether it's faster or not for you will depend on your hardware, the size of your arrays and probably the version of matlab that you're using too.

类别

在 Help Center 和 File Exchange 中查找有关 Linear Algebra 的更多信息

标签

产品


版本

R2021a

Community Treasure Hunt

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

Start Hunting!

Translated by