Plotting from .dat file in Octave

Question

I am running a Fortran code that is outputting several sets of data to one .dat file. I want to plot the data, which is in two columns, using Octave. For example, the data I want to plot is in the following form:

      t              Eta(t)
     0.00           -0.748
     0.50           -0.773
     1.00           -0.774
     1.50           -0.535
     2.00           -0.120
     2.50            0.131
     3.00            0.184
     3.50            0.211
     4.00            0.068
     4.50           -0.110

Where the data starts on line 148 (not including the t and eta(t) line) and continues until line 247. The data for t and eta(t) obviously span across a few columns (according to the text file, that's where I'm reading the lines and column numbers from). Is there any way to plot the data if it's in this form by specifying which line to start from or anything? Put simply, I want to plot it so that the values in the t column are on the x axis and the eta(t) values are on the y axis. Thanks in advance for any help!

ederag ederag · Accepted Answer · 2014-10-02T19:21:57

A much faster alternative to textread (see Andy's answer) is dlmread.

filename = "yourfile.dat";
# empty separator means 'automatic'
separator = '';
skipped_rows = 147;
skipped_columns = 0;
m = dlmread(filename, separator, skipped_rows, skipped_columns);
t = m(:,1);
eta_ = m(:, 2);
plot(t, eta_)

If you want to stop reading the file after line 248, use

filename = "yourfile.dat";
# empty separator means 'automatic'
separator = '';
skipped_rows = 147;
skipped_columns = 0;
last_row = 248
last_column = 2
m = dlmread(filename, separator, 
            [skipped_rows, skipped_columns, last_row-1, last_column-1]);
t = m(:,1);
eta_ = m(:, 2);
plot(t, eta_)

Plotting from .dat file in Octave

2 Answers