Same procedure for different matrices

2017 7 26
1 个回答
更新时间：2017 7 26
2 次查看（30 天）

0 个投票

Hey there, I'm not good with writing loops and I guess I need one for my problem. I have a couple of matrices of different sizes that I would like to split into quadrants and then take the average of all non-zero elements for each quadrant which I am able to do with the following code:
B = A(1:(mod(end, 2)==1)*0.5+end/2, 1:(mod(end, 2)==1)*0.5+end/2);
C = A(1:(mod(end, 2)==1)*0.5+end/2, (mod(end, 2)==1)*0.5+end/2+ 1:end);
D = A(end/2+(mod(end, 2)==1)*0.5 + 1:end, 1:(mod(end, 2)==1)*0.5+end/2);
E = A(end/2+(mod(end, 2)==1)*0.5 + 1:end, end/2+(mod(end, 2)==1)*0.5+ 1:end);
avg_A(:,:) = [mean(B(B(:)>0)) mean(C(C(:)>0)); mean(D(D(:)>0)) mean(E(E(:)>0))];
where A is the first of many matrices. Now, my question is, whether I can apply that code to all my other matrices (A2,A3,A4,...) without copying this code and change all the "A"s to "A2"s and so on. In the end I would like to have a matrix of size 2x2xnumber of matrices.
Hope you have enough information and can help me with that.

3 个评论
显示 1更早的评论 隐藏 1更早的评论

Stephen23
Stephen23 2017-7-26
编辑：Stephen23 2017-7-26
Do NOT waste your time writing bad code that creates or acceses separate variables with numbered variable names: "A frequent use of the eval function is to create sets of variables such as A1, A2, ..., An, but this approach does not use the array processing power of MATLAB and is not recommended."
source: http://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html
Just use indexing: simple, fast, efficient, neat, simple, easy to understand, much less buggy, easier to debug, etc, etc, etc.
https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval
https://www.mathworks.com/matlabcentral/answers/143-how-do-i-make-a-series-of-variables-a1-a2-a3-a10
https://www.mathworks.com/matlabcentral/answers/57445-faq-how-can-i-create-variables-a1-a2-a10-in-a-loop
etc, etc, etc.
"whether I can apply that code to all my other matrices (A2,A3,A4,...) without copying this code"
Yes, when you put all of those arrays into one ND-array or cell array, and then simply loop over it using indexing. Note that your code may also be best put into a function.
Felix Koenig
Felix Koenig 2017-7-26
First of all, thank you for your answer. Don't worry, I'm using indices, I just wrote A2,A3,.. for simplicity here.
I really am a matlab greenhorn, but as far as I know, I don't think I can put all my arrays into one, since they all have different dimensions. So A_1 would be a 23x24 matrix, A_2 would be 22x25 and so on. If there is a way to put them all into one array, please show me how to do that.
My plan was to split those matrices into quadrants first (if the number of rows or columns is odd, it's alright for one quadrant to be larger than another one) and then calculate an average for each quadrant. That way I get multiple 2x2 matrices that I can all put into one array.
Please correct me if that is wrong thinking.
Jan
Jan 2017-7-26
Use a cell array instead as a container for arrays of different size:
A = {rand(23, 25), rand(22,25)};
size(A{1})
size(A{2})

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Jan
Jan 2017-7-26
编辑：Jan 2017-7-26

0 个投票

Use a subfunction:
A = {rand(23, 25), rand(22,25)};
B = zeros([2, 2, numel(A)]);
for iA = 1:numel(A)
B(:, :, iA) = QuadrantMean(A{iA});
end
function M = QuadrantMean(A)
S = floor(size(A) / 2);
A11 = A(1:S(1), 1:S(2));
A12 = A(1:S(1), S(2)+1:end);
A21 = A(S(1)+1:end, 1:S(2));
A22 = A(S(1)+1:end, S(2)+1:end);
M = [mean(A11(A11 ~= 0)), mean(A12(A12 ~= 0)); ...
mean(A21(A21 ~= 0)), mean(A22(A22 ~= 0))];
end

类别

在 帮助中心 和 File Exchange 中查找有关 Matrix Indexing 的更多信息

标签

编辑：

Jan
Jan
2017-7-26

Community Treasure Hunt

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

Start Hunting!

Translated by