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

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

[Abhilash Padma]

what is the format of data present in text file?

[Shuvashish Roy]

It is a .txt file. Please see the attached text file in the question. Thanks.

[Abhilash Padma]

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

[Turlough Hughes]

It looks like the first line corresponds to i j and the fifth to Dx Dy.

Answer 1

[Turlough Hughes]

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.

[Shuvashish Roy]

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

Answer 2

[Turlough Hughes]

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];

[Shuvashish Roy]

Hi, Turlough,

Thanks a lot for your prompt reponse. You are such a helpful person. By the way, If I want to read the fourth line instead of the fift line, how should I change the code?

Lets think the output be like this:

I J DX DY

2 2 963371.99 1383093.75

3 2 963407.53 1383093.75

.................................................... ...............

...................................................................

197 199 970301.61 1393325.93

Thanks.

[Shuvashish Roy]

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');

[Turlough Hughes]

Change

mod(c,5)==0

to

mod(c+1,5)==0