How to select columns from data matrix using "for" loop?

Hi,

I would like to select columns from a data matrix and use them to interpolate data from another file. For example, first column is selected and interpolated from another file, and printed, then the second column, and so on. I know the interpolation code, but I need the selection of column and printing the interpolated data codes.

I would be grateful if someone can help me in this.

Thank you. Regards, Ismail

Answer 1

[Birdman]

One approach:

for i=1:size(A,2)%number of columns
    b=A(:,i);%ith column is assigned to b variable at every step
    interp(b,..);%you can use it in your function 
end

[Birdman]

Either erase the semicolon:

for i=1:size(A,2)%number of columns
    b=A(:,i)
    interp(b,..);
end

or use disp:

for i=1:size(A,2)%number of columns
    b=A(:,i);%ith column is assigned to b variable at every step
    interp(b,..);%you can use it in your function 
    disp(b)
end

[Ismail Qeshta]

Thanks Birdman. Would you please be able to suggest to me how to print the outcome out at every step?

[Birdman]

Outcome, means outcome of interp? Then:

for i=1:size(A,2)%number of columns
    b=A(:,i);%ith column is assigned to b variable at every step
    res=interp(b,..);%you can use it in your function 
    disp(res)
end

[Birdman]

I mean to print the interpolation results in a .txt file.

Answer:

for i=1:size(A,2)%number of columns
    b=A(:,i);%ith column is assigned to b variable at every step
    res=interp(b,..);%you can use it in your function 
    disp(res)
    fid=fopen(['result_' num2str(i) '.txt'],'w');
    fprintf(fid,'%f\n',res); 
    fclose(fid)
end

[Ismail Qeshta]

Thank you very much Birdman for the code. That is really helpful. Also, I am actually extracting the data matrix from a file. I am not sure how to modify the code to suit that. Thank you again Birdman for your great help.

[Walter Roberson]

Unless you have a different data matrix file for each column, you would read the data once before the loop, and then (if necessary) extract the appropriate portion of it inside the loop.

[Birdman]

You will use fscanf instead of fprintf. Imagine you want to read the file you wrote. Simply do this:

    fid=fopen('result_1.txt,'r');
    fscanf(fid,'%f') 
    fclose(fid)

The line with fscanf will display the result of the txt file.

[Ismail Qeshta]

Many thanks Birdman. I tried to incorporate it in my code. I only get the interpolation in the first file. Would you please be able to check it for me?

clear; clc;
Folder = cd;
N=100;
x2     = zeros(N, 10);
for k = 1:N;
  Driftt  = sprintf('Drift%d.out', k);
  Reactt  = sprintf('React%d.out', k);
  matDrift     = importdata(fullfile(Folder, Driftt));
  matReact = importdata(fullfile(Folder, Reactt));
  x1= matDrift(:,2);
  y1= -sum(matReact(:,2:11),2);

[x3, ix] = unique(x1);
y3       = y1(ix);
A=importdata('allPiers.txt');
for i=1:size(A,37)%number of columns
    b=A(:,i);%ith column is assigned to b variable at every step   
[y2] = [b];
x2 (k,:) = interp1(y3, x3, y2, 'linear')
 fid=fopen(['result_' num2str(i) '.txt'],'w');
 fprintf(fid,'%f\n',x2); 
 fclose(fid)
end
end

[Birdman]

i=1:size(A,37)

The above has to change to

i=1:size(A,2)

[Ismail Qeshta]

Great. Thank you so much Birdman. The only thing is that some of the data in the .txt files are written as "NaN". Is there anyway to replace them automatically with 0.07?

[Birdman]

Replace them before writing in your for loop. So

temp=x2(k,:);
temp(isnan(temp))=0.07;
x2(k,:)=temp;

and then write to the txt file.

[Ismail Qeshta]

Thank you Birdman. Which one exactly? I put it before the second for loop but it does not work.

[Ismail Qeshta]

I actually mean the output "result_n.txt" files.

[Birdman]

Use the following code:

clear; clc;
Folder = cd;
N=100;
x2     = zeros(N, 10);
for k = 1:N;
  Driftt  = sprintf('Drift%d.out', k);
  Reactt  = sprintf('React%d.out', k);
  matDrift     = importdata(fullfile(Folder, Driftt));
  matReact = importdata(fullfile(Folder, Reactt));
  x1= matDrift(:,2);
  y1= -sum(matReact(:,2:11),2);
[x3, ix] = unique(x1);
y3       = y1(ix);
A=importdata('allPiers.txt');
for i=1:size(A,37)%number of columns
    b=A(:,i);%ith column is assigned to b variable at every step   
[y2] = [b];
x2 (k,:) = interp1(y3, x3, y2, 'linear')
temp=x2(k,:);
temp(isnan(temp))=0.07;
x2(k,:)=temp;
 fid=fopen(['result_' num2str(i) '.txt'],'w');
 fprintf(fid,'%f\n',x2); 
 fclose(fid)
end
end

[Ismail Qeshta]

Many thanks Birdman. Shall the for i=1:size(A,37) be changed to i=1:size(A,2)?

[Birdman]

Oh yes, change it.

[Ismail Qeshta]

I cannot thank you enough Birdman. You have been awesome. Thank you very much.

[Birdman]

You are welcome.

[Ismail Qeshta]

Hi Birdman. Actually, after doing some further checking of the code, I found that it does not give the same results as when I use it for individual columns using the original code below. Would you please be able to help me find the error?

clear; clc;
Folder = cd;
N=100;
x2     = zeros(N, 10);
for k = 1:N;
  Driftt  = sprintf('Drift%d.out', k);
  Reactt  = sprintf('React%d.out', k);
  matDrift     = importdata(fullfile(Folder, Driftt));
  matReact = importdata(fullfile(Folder, Reactt));
  x1= matDrift(:,2);
  y1= -sum(matReact(:,2:11),2);

[x3, ix] = unique(x1);
y3       = y1(ix);

[y2] = [8479186.526  5814080.3  7648088.256  7116870.805  9233172.585];
x2 (k,:) = interp1(y3, x3, y2, 'linear')

end

[Birdman]

x2 (k,:)

The above refers to individual rows. You need to write it as

x2 (:,k)

[Ismail Qeshta]

Thanks Birdman. It showed me the following error message: Subscripted assignment dimension mismatch.

Subscripted assignment dimension mismatch.

Error in Interpolate11 (line 18)
x2 (:,k) = interp1(y3, x3, y2, 'linear')

[Birdman]

Write this:

x2 (:,k) = interp1(y3, x3, y2, 'linear').'

[Ismail Qeshta]

Thanks Birdman. I got the same error message as above. Now the code is:

clear; clc;
Folder = cd;
N=100;
x2     = zeros(N, 10);
for k = 1:N;
  Driftt  = sprintf('Drift%d.out', k);
  Reactt  = sprintf('React%d.out', k);
  matDrift     = importdata(fullfile(Folder, Driftt));
  matReact = importdata(fullfile(Folder, Reactt));
  x1= matDrift(:,2);
  y1= -sum(matReact(:,2:11),2);
[x3, ix] = unique(x1);
y3       = y1(ix);
A=importdata('AllPiers2.txt');
for i=1:size(A,2)%number of columns
    b=A(:,i);%ith column is assigned to b variable at every step   
[y2] = [b];
x2 (:,k) = interp1(y3, x3, y2, 'linear').'
temp=x2(:,k);
temp(isnan(temp))=0.07;
x2(:,k)=temp;
 fid=fopen(['result_' num2str(i) '.txt'],'w');
 fprintf(fid,'%f\n',x2); 
 fclose(fid)
end
end

[Birdman]

What does the output of

interp1(y3, x3, y2, 'linear')

look like?

[Ismail Qeshta]

This interpolation is for getting the y values that correspond to x values from the data matrix column. It refers to the linear interpolation.

[Birdman]

What is the size(dimensions) of it?

[Ismail Qeshta]

I don't know, but the output of x2 is 10 X 100.

[Birdman]

clear; clc;
Folder = cd;
N=100;
x2     = zeros(N, 10);
for k = 1:N;
  Driftt  = sprintf('Drift%d.out', k);
  Reactt  = sprintf('React%d.out', k);
  matDrift     = importdata(fullfile(Folder, Driftt));
  matReact = importdata(fullfile(Folder, Reactt));
  x1= matDrift(:,2);
  y1= -sum(matReact(:,2:11),2);
[x3, ix] = unique(x1);
y3       = y1(ix);
A=importdata('AllPiers2.txt');
for i=1:size(A,2)%number of columns
    b=A(:,i);%ith column is assigned to b variable at every step   
[y2] = [b];
res = interp1(y3, x3, y2, 'linear').'
x2=res(:,k);
temp=x2;
temp(isnan(temp))=0.07;
x2=temp;
 fid=fopen(['result_' num2str(i) '.txt'],'w');
 fprintf(fid,'%f\n',x2); 
 fclose(fid)
end
end

[Ismail Qeshta]

Many thanks Birdman. I got the following error message:

Index exceeds matrix dimensions.

Error in Interpolate11 (line 19)
x2=res(:,k);

[Birdman]

Ups, I missed this. Adapt this code:

clear; clc;
Folder = cd;
N=100;
x2     = zeros(N, 10);
for k = 1:N;
  Driftt  = sprintf('Drift%d.out', k);
  Reactt  = sprintf('React%d.out', k);
  matDrift     = importdata(fullfile(Folder, Driftt));
  matReact = importdata(fullfile(Folder, Reactt));
  x1= matDrift(:,2);
  y1= -sum(matReact(:,2:11),2);
[x3, ix] = unique(x1);
y3       = y1(ix);
[y2] = [8479186.526  5814080.3  7648088.256  7116870.805  9233172.585].';
x2 (k,:) = interp1(y3, x3, y2, 'linear')
end

[Ismail Qeshta]

Many thanks Birdman. In which part of the code should it be placed? This code is for individual data not the one we discussed above I think.

[Birdman]

clear; clc;
Folder = cd;
N=100;
x2     = zeros(N, 10);
for k = 1:N;
  Driftt  = sprintf('Drift%d.out', k);
  Reactt  = sprintf('React%d.out', k);
  matDrift     = importdata(fullfile(Folder, Driftt));
  matReact = importdata(fullfile(Folder, Reactt));
  x1= matDrift(:,2);
  y1= -sum(matReact(:,2:11),2);
[x3, ix] = unique(x1);
y3       = y1(ix);
A=importdata('AllPiers2.txt');
for i=1:size(A,2)%number of columns
    b=A(:,i);%ith column is assigned to b variable at every step   
[y2] = [8479186.526  5814080.3  7648088.256  7116870.805  9233172.585].';
x2 (:,k) = interp1(y3, x3, y2, 'linear').'
temp=x2(:,k);
temp(isnan(temp))=0.07;
x2(:,k)=temp;
 fid=fopen(['result_' num2str(i) '.txt'],'w');
 fprintf(fid,'%f\n',x2); 
 fclose(fid)
end
end

[Ismail Qeshta]

Thanks Birdman. [y2] should take [b] values not the one inserted. Isn't it?

[Ismail Qeshta]

I still got the same error message:

Subscripted assignment dimension mismatch.

Error in Interpolate11 (line 18)
x2 (:,k) = interp1(y3, x3, y2, 'linear').'

[Birdman]

Make sure that this y2 vector you defined manually has the same length with

   b=A(:,i);
   y2=b;

because that was working as I recall. Notice the lengths should be equal.

[Ismail Qeshta]

It was actually working, but the results were unfortunately different.

[Ismail Qeshta]

The matrix dimension problem came up only when we started changing the x2(:,k) with x2(k,:)

[Birdman]

Then keep the initial order. :)

[Ismail Qeshta]

Thanks Birdman. Yes, that is right, but how to fix the difference in results?

[Birdman]

Maybe that should be another question in forum, right?

[Ismail Qeshta]

Yes. I was thinking about that. Thank you very much again Birdman. I really appreciate your time and effort.

[Birdman]

You are welcome.