Read spesific rowintervals from .txt file and store them

I am trying to read a large .txt doc that continues for maany rows. I have tried to do it manually by the following code:

for i = 12
    C = textscan(fid,'%.6f %.6f',npoints,'delimiter','\n', 'headerlines',i-1);
    p1 = C{1}*1e3;
    y1 = C{2};
    py1 = [p1 y1];
end
for i = 40
    C = textscan(fid,'%.6f %.6f',npoints,'delimiter','\n', 'headerlines',i-1);
    p2 = C{1}*1e3;
    y2 = C{2};
    py2 = [p2 y2];
end
for i = 68
    C = textscan(fid,'%.6f %.6f',npoints,'delimiter','\n', 'headerlines',i-1);
    p3 = C{1}*1e3;
    y3 = C{2};
    py3 = [p3 y3];
end

Is it possible to do this is one loop ? the number of rows are equal for all the "intervals" such that "npoints" is fixed 21. and it is 28 spaces between each interval so I was thinking something like for i = [12:28:1356] where 1356-1376 is the last interval.

Answer 1

[KSSV]

I = [12 40 68] ; 
iwant = cell(length(I),1) ; 
for i = 1:length(I)
    C = textscan(fid,'%.6f %.6f',npoints,'delimiter','\n', 'headerlines',I(i)-1);
    p1 = C{1}*1e3;
    y1 = C{2};
    py1 = [p1 y1];
    iwant{i} = py1 ; 
end

[Henning Eimstad]

Thanks! I really like how it gets structured. But I get the same problem as my manual code... row 12-32 is the only one that is read properly as a 21x2 which is want I want. The next ones are not the correct numbers and are stored as 18x2 and 16x2 respectively for line 40 and 68.

[KSSV]

You have to check your I values.

[Henning Eimstad]

Well, it works when I check for just I = 12, I = 40 etc, but it doesnt work with I = [12 40 68 ..... ]. Cant see why that should be a problem?

[Henning Eimstad]

For some reason, the first value read for line 40 when I use I = [12 40] is from line 72 and not 40...