Error in my simple code, 3d matrix issue

Question

Robert 2015-4-14

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/203040-error-in-my-simple-code-3d-matrix-issue

评论： Image Analyst 2015-4-15

Here is my code. Basically I am trying to load in 31 matrices then produce one new matrix that is the element by element average of all 31 (So in the new matrix 1:1,1:1 will be the average of the 31 1:1,1:1 values). There is an error somewhere, I think where I make the 2D matrices into 1 3D matrix. The code runs but result is wrong (the matrix that is compiled does not represent the 31 original matrices)

clear all
%Load the Data
S = dir('*.txt');
N = {S.name};
k = 1:numel(S)
A = load(N{k});
Days=zeros(35,43,31);
for k=1:31
Days(:,:,k)=rand(35,43);
end
%Find the Average
Janmean = mean(Days, 3);
%Export the Data
dlmwrite('200301.txt',Janmean)

Thank you in advance for any alterations/help

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Guillaume 2015-4-15

在 MATLAB Online 中打开

A note on a part of your code that made me pause:

N = somecellarray
k = 1:numel(N); %you use S but N is the same szie
N{k}

is the same as

N = somecellarray
N{:}

The latter shows your intent a lot better

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Jan 2015-4-14

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/203040-error-in-my-simple-code-3d-matrix-issue#answer_175134

编辑：Jan 2015-4-14

在 MATLAB Online 中打开

When you omit the evil clear all you can use the debugger to examine your code line by line. The debugger is such useful and required for serious programming, that dleteing all breakpoints is an extremely bad side effect of clear all.

With the debugger you would see, that the load does not do, what you expect. In the loop the values are set to random matrices by the rand command and the loaded data are simply ignored.

    Days = zeros(35,43,31);
  for k = 1:31
    Data = load(N{k});
    Days(:,:,k) = Data.Value;  % Replace "Value" according to you files
  end

4 个评论
显示 2更早的评论隐藏 2更早的评论

Robert 2015-4-15

在 MATLAB Online 中打开

Thanks, but still stumped, if I only put one variable name in the code won't it just use the same one every loop? I have altered the code but still having trouble...

%This code is to calculate the monthly average from daily values in each
%pixel
clear all
%Load the Data
S = dir('*.txt');
N = {S.name};
k = 1:numel(S)
 Days = zeros(35,43,31);
  for k = 1:31
    Data = load(N{k});
    Days(:,:,k) = (Data.???);  
  end
%Find the Average
Janmean = mean(Days, 3);
%Export the Data
dlmwrite('200301.txt',Janmean)

Image Analyst 2015-4-15

Did you see the FAQ I gave in my answer? It doesn't use the same filename on each iteration.

请先登录，再进行评论。

Answer 2

Image Analyst 2015-4-15

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/203040-error-in-my-simple-code-3d-matrix-issue#answer_175276

Attach one of your text files. If they are not .mat format files then you should probably use some other function instead of load(), like csvread(), importdata(), readtable(), textscan() or something like that.

And see the FAQ for how to read a sequence of files: http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

3 个评论
显示 1更早的评论隐藏 1更早的评论

Image Analyst 2015-4-15

What a mess. Does load() read that in correctly?????

Robert 2015-4-15

Absolutely, each file loads as a 35x43 matrix. This is the way the data is provided to me

请先登录，再进行评论。

Answer 3

Guillaume 2015-4-15

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/203040-error-in-my-simple-code-3d-matrix-issue#answer_175287

编辑：Guillaume 2015-4-15

在 MATLAB Online 中打开

Your original code would never work because when you write

load(N{k})

you're passing all the filenames to load at once. load can only open one file at a time. Therefore as per Jan's example your load needs to be inside a loop.

Secondly, I believe that Jan and Image Analyst missed the fact that your load is loading a text file instead of a mat file (or like me assumed it behaved the same for text as for mat, I had to look up the doc). With mat files, load creates a structure whose field names are the variable names stored in the files (hence the replace "Value" according to your file comment). With text files, load just load the data as a matrix.

You were actually nearly there, you'd just need to move the load inside loop and get rid of the rand stuff (what is that about anyway):

%Load the Data
S = dir('*.txt');
numdays = numel(S);
%no need to convert the structure into a cell array
Days=zeros(35,43, numdays); %this is more flexible than hard coding the number of days, particularly if you never check that you actually have 31 files.
for day = 1:numdays  %again avoid hardcoding constants, also use better variable names
    daydata = load(S(day).name);
    %When dealing with user input / data loaded from files, always check that it conforms to your expectations:
    assert(isequal(size(daydata), [35 43]), 'File %s is not a 35x43 matrix', S(day).name);
    Days(:, :, day) = datdata;
end
%Find the Average
Janmean = mean(Days, 3);
%Export the Data
dlmwrite('200301.txt',Janmean)

As per my comments in the code, you're dealing with external input (in this case files) which may not actually be what you expect. For example there may be 32 text files in the directory, or one of the file may not be a 35 x 43 matrix. When you deal with external input, it's always a good idea to check that it conforms to your expectation or not hard code these expectations.