creating matrix out of another matrix

3 次查看（过去 30 天）

mehra 2019-9-9

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/479513-creating-matrix-out-of-another-matrix

评论： mehra 2019-9-9

I have a results matrix of size 104*14. I want to create a matrix of size 8*13 in which u(1,1)=results((1:13),4) and....I tried to write the matrix like:

u_mean_Uund=[results(1:13),4; results(14:26),4;results(27:39),4;results(40:52),4;results(53:65),4;...
    results(66:78),4;results(79:91),4;results(92:104),4]

But this shows the first column of the results matrix, I actually want a 8*13 matrix in which the arrays are all from column 4.

2 个评论
显示无隐藏无

Stephen23 2019-9-9

Your description contradicts itself: "I want to create a matrix of size 8*13..." but also "I actually want a 8*14 matrix...": so do you want an 8x13 or an 8x14 matrix?

mehra 2019-9-9

Check my edited answer.

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

mehra 2019-9-9

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/479513-creating-matrix-out-of-another-matrix#answer_391055

在 MATLAB Online 中打开

I solved it using following for loop:

for nn=1:8
    u_depth(nn,:)=transpose(results((13*(nn)-12):13*(nn),4));
end

4 个评论
显示 2更早的评论隐藏 2更早的评论

Bruno Luong 2019-9-9

编辑：Bruno Luong 2019-9-9

在 MATLAB Online 中打开

"I explained why the older comment doesn't give the answer"

And Stephen has explained to you the opposite and I tested it

results=rand(104,14);
% your solution
for nn=1:8
u_depth(nn,:)=transpose(results((13*(nn)-12):13*(nn),4));
end
% Stephen's solution
out = reshape(results(:,4),13,8).';
isequal(u_depth,out)

It returns 1, meaning both gives the same ANSWER on a random input. So Stephen is right and you are wrong.

You just are not rigouruous person and lack patient or perhaps a bit of courtesy to discuss with Stephen.

mehra 2019-9-9

Well... I dont know niether you nor Stephen and I dont want to argue with anyone...i was rushing to get the answer as soon as possible, so I also worked on that... Anyway i think you cant judge people like this...and again I thanks everyone for their answers and their help.

请先登录，再进行评论。

更多回答（1 个）

Stephen23 2019-9-9

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/479513-creating-matrix-out-of-another-matrix#answer_390997

编辑：Stephen23 2019-9-9

在 MATLAB Online 中打开

out = reshape(results(:,4),13,8).';
out(:,14) = 4; % if you want an 8x14 matrix

10 个评论
显示 8更早的评论隐藏 8更早的评论

Stephen23 2019-9-9

编辑：Stephen23 2019-9-9

"actually ıt should be out=reshape(results(:,4),8,13) since İ need 8 rows and 13 columns but"

No it shouldn't be.

MATLAB stores arrays in column-major order, which is why I reshaped to size (13,8) and then used transpose. You totally ignored the transpose I used, which means that you will get all of your data going down the columns first... which is definitely not what you requested.

"I think the reshape command wouldnt work here because in reshape it takes the first 8 data and then the next 8 data ..."

Actually reshape works fine, exactly the way I used it in my answer.

They way you used it will not work (in exactly the way that you describe).

"in fact I want the first 13 data of column 4 to make my 1st row which includes 13 columns and then the next 13 data should build my next row containing 13 columns and so on"

Which is exactly what the code in my answer does (note: this is not the same as your code).

"how can I write it in a shorter way and in one copact code?"

I would use the code in my answer (not your incorrect code).

Stephen23 2019-9-9

在 MATLAB Online 中打开

"...but still you have not seen my problem..."

If I failed to understand your problem as you claim, how did I write code that returns exactly the same result as your loop (which you posted four hours later)?

>> results = rand(104,14);
>> for nn=1:8 % your loop
u_depth(nn,:)=transpose(results((13*(nn)-12):13*(nn),4));
end
>> out = reshape(results(:,4),13,8).'; % my simpler reshape
>> isequal(u_depth,out) % The same outputs!
ans =
     1

That would require me to make two mistakes:

to misunderstand your question (which is certainly possible),
then to write strangely buggy MATLAB code that doesn't do what I want it to do (based on my incorrect understanding of your problem), but that coincidentally ends up doing exactly the same thing as your loop....

With such luck, I should go an buy a lotto ticket!

mehra 2019-9-9