Extracting data from txt file

Hi, I have a raw data file where there's two variable - F & R. I would like to extract the specific value of R when F is at 5, 10, 15, 20. what should I do? Please help me with the coding. I'm new in Matlab. Thank you.

[Walter Roberson]

What does the data file look like? Please be specific about information such as whether it is tab separated columns.

Will those exact values of F appear in the file, or do you need to interpolate the values?

Answer 1

[Walter Roberson]

filename = 'AppropriateFileName';

data = sortrows( load(filename) );
F = data(:,1);
R = data(:,2);

probe_at = 5:5:20;

interpolated_R = interp1(F, R, probe_at);

I note that you want F at 15 and 20, which are beyond the range of F in the sample you post. If the data does not extend as far as 15 or 20 then the above code would return NaN in those positions. Extrapolation is possible by adding extra options to the interp1() call, but you should consider more about what kind of extrapolation is appropriate; I can see that you have something non-linear going on in the response.