For loop to write data to excel

Question

Zhenhui 2012-6-17

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/41336-for-loop-to-write-data-to-excel

I have a number of matrix (e.g. n=10) dw1,dw2....dw10. they are obtained through equation dw=-dudx-dvdy. I want to use a for loop to write all these matrix to an excel. I did these

for i = 1:n;
    dwname = sprintf('dw%d=-dudx%d-dvdy%d;',[i,i,i]);
    eval(dwname);
    xlswrite('name.xls',dwname,i,'a1:a600');
end

From this loop i got all the dwi. but because dwname is a char, so the data wrote to excel is not the matrix dwi not only a string . I tried to transfer the char name to variable, but didnt make it.

Is there anyone who can help me with this?

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Answer 1

Image Analyst 2012-6-17

2
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https://ww2.mathworks.cn/matlabcentral/answers/41336-for-loop-to-write-data-to-excel#answer_50953

在 MATLAB Online 中打开

dwname needs to be a cell, not a character array. Put it inside braces like this {dwname}. Or better yet do it this way where I first create the cell array and then write it out just once at the end instead of in every iteration:

% Create a 1 by n cell array called dwname.
n = 5;
for i = 1:n
  dwname{i} = {sprintf('dw%d=-dudx%d-dvdy%d;',[i,i,i])}
end
% Write out the cell array all in one shot.
sheetNumber = 1;
range = 'a1';
xlswrite('name.xls', dwname, sheetNumber, range);

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Zhenhui 2012-6-17

hi, thanks a lot for the help.

i tried this. but the cell dwname only have the names of 'dw1=-dudx1-dvdy1; ''dw2=-dudx2-dvdy2;'... I didnt see the data. and it is also all blank in excel. i don't know what is the problem.

sorry that i don't have much experience in Matlab. Maybe it is better explain the thing i want to achieve.

Actually I am dealing with PIV image data. I got the velocity data of u, v in many parallel (n) planes. For the u,v in plane i, they are store in sheeti in excel filename.xls. I have to read all the data in all planes and do the surface fitting and then get the dw=-dudx-dvdy.

The code i use is :

% read data from PIV measurement

% input of x, y, u and v

filename='270H-O.xls';

x=xlsread(filename,'1','a1:a639');

y=xlsread(filename,'1','b1:b639');

n=10; % select n parallel planes

rows=639; % data rows

u=zeros(rows,n);

v=zeros(rows,n);

% I put all the u or v in one matrix

for i = 1:n;

sheetname=num2str(i);

u(:,i)=xlsread(filename,sheetname,'e:e');

v(:,i)=xlsread(filename,sheetname,'g:g');

end

%%surface fitting and calculate derivatives du, dv, dw

for i = 1:n;

ufitname = sprintf('fu%d=createSurfaceFit2(x,y,u(:,i));',i);

eval(ufitname);

duname=sprintf('[dudx%d,dudy%d]=differentiate(fu%d,x,y);',[i,i,i]);

eval(duname);

vfitname = sprintf('fv%d=createSurfaceFit2(x,y,v(:,i));',i);

eval(vfitname);

dvname=sprintf('[dvdx%d,dvdy%d]=differentiate(fv%d,x,y);',[i,i,i]);

eval(dvname);

dwname = sprintf('dw%d=-dudx%d-dvdy%d;',[i,i,i]);

eval(dwname)

end

until here I got dwi in all 10 planes and I can see these matix in workspace. But now I got problems to write these dw back to the excel in which plane they came from. That is I want to write dwi to filename. Xls, sheeti, newrange

Sorry for the long text. Hope you can help .

Cheers

Hui

Image Analyst 2012-6-18

I don't have your data files, or Excel on this computer, so I can't test anything. All I can say is to start with my code and then look at the example in the help for xlswrite to learn how you can construct a cell array that has both numbers and strings. One cell of the cell array can contain either a string (multiple characters), or a single number of an array. The cell cannot contain the entire array if I remember correctly - you have to put each element into its own cell.

Zhenhui 2012-6-18