Reading/Extracting data from a text file in a certain format using Matlab

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Shuvashish Roy
Shuvashish Roy 2019-10-1
编辑： Shuvashish Roy 2019-10-8
Hi,
I am a beginner in Matlab. I need to extract some required data [ I index, J index of cells and their lengths(DX) and widths(DY)] from the attached text file in the following formate:
I J DX DY
2 2 35.53 51.93
3 2 35.53 51.93
4 2 35.53 51.93
5 2 35.53 51.93
.............................................
.............................................
196 199 35.53 51.93
197 199 35.53 51.93
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Abhilash Padma
Abhilash Padma 2019-10-4
But data is not clear in text file. Below are the first few lines of text file. Could you explain what each line corresponds to?
2 2 963354.2231605511624366963389.7596605512080714963389.7596605512080714963354.2231605511624366
1383067.78205397375859321383067.78205397375859321383119.72205397370271381383119.7220539737027138
963371.9914105511270463 1383093.7520539737306535
35.5365000000409808 51.9399999999999977

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Turlough Hughes
Turlough Hughes 2019-10-4
Hi Shuvashish,
If i'm correct in my understanding of your data, it looks like you want to take the first and fifth line of data for every 5 lines in your text file.
You could try reading the text file line by line using fgetl(). This returns the next line of your file as a character vector, then use str2num() to convert your character vector to a 1x2 array in this case. I've added in conditions to store only the lines you specified. Note that you need to have waterscape2.txt in your current working directory or else filename has to be changed, for example filename='C:\...\waterscape2.txt'.
filename='waterscape2.txt'
fid = fopen(filename);
fgetl(fid); %read first line of text file
tline=fgetl(fid); %read second line
c=0; ij=[]; DxDy=[];
while ischar(tline)
c=c+1;
if mod(c+4,5)==0 % store when c=1,6,11,...,etc.
ij(end+1,1:2)=str2num(tline);
end
if mod(c,5)==0 % store when c=5,10,15,...,etc.
DxDy(end+1,1:2)=str2num(tline);
end
tline = fgetl(fid);
end
fclose(fid)
data=[ij DxDy];
Aside from fgetl there is also some relevant documentation here for reading data line-by-line.
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Shuvashish Roy
Shuvashish Roy 2019-10-8
thank you so much for your help, It worked ! However, would you please explain how the "end+1" works in storing data inside ij and DXDY :) Again, how to modify the code If I want to insert another two columns in the matrix with some constant values (i.e. 5 & 3). ?
Let's think the output matrix should be the following:
I J DX DY DM DN
2 2 35.53 51.93 5 3
3 2 35.53 51.93 5 3
4 2 35.53 51.93 5 3
5 2 35.53 51.93 5 3
.................................................... ...............
...................................................................
196 199 35.53 51.93 5 3
197 199 35.53 51.93 5 3

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Turlough Hughes
Turlough Hughes 2019-10-8
编辑：Turlough Hughes 2019-10-8
No problem.
On your first question; The last index of an array can be specified by calling the index end. end + 1 means we add an additional row at the end of the arrays ij and DxDy to save the new lines read from your file. It might be helpful for you to look up matrix indexing in the documentation or the following video.
For the second question, one way is to do the following:
DMDN = ones(size(ij));
DMDN(:,1)=DMDN(:,1).*5;
DMDN(:,2)=DMDN(:,2).*3;
data = [data DMDN];
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Shuvashish Roy
Shuvashish Roy 2019-10-8
编辑：Shuvashish Roy 2019-10-8
Thanks Turlough,
I have figured it out.
filename='waterscape2.txt'
fid = fopen(filename);
fgetl(fid); %read first line of text file
tline=fgetl(fid); %read second line
c=0; ij=[]; DxDy=[];
while ischar(tline)
c=c+1;
if mod(c+4,5)==0 % store when c=1,6,11,...,etc.
ij(end+1,1:2)=str2num(tline);
end
if mod(c+1,5)==0 % store when c=5,10,15,...,etc.
DxDy(end+1,1:2)=str2num(tline);
end
tline = fgetl(fid);
end
fclose(fid)
data=[ij DxDy];
save('efdclxly.txt','data','-ascii');

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