Plotting ASCII files in ROOT

Question

I am trying to write a small macro that reads data from an ASCII file that has 4 columns. But I want to graph only the second the third columns as (x, y).

Answer 1

The constructor of TGraph can directly take a CSV file, see the documentation.

TGraph g("data.csv", "%*lg %lg %lg %*lg", ",");

The first argument is the filename, and the second argument a format string. Skipped columns are denoted with a *; to skip the last column you could actually just omit it from the format string,

%*lg %lg %lg

The third argument is the column separator which might be , for your flavor of CSV.