How to plot piecewise function using data plot in Gnuplot?

Question

According to figure above. this picture is generated from data points in text file. My question is that how can i remove the line at any two points if graph is jumped? (In my picture see that graph is jump about on x~260)

note that my purpose is that i just want to make this graph look like piecewise function that mean line on the middle of graph should not be connected because is jumped.

Answer 1

In gnuplot you can split a line in several parts either when you have an invalid data value somewhere, or an empty line.

For the first situation, you could check inside the using statement, if the difference to the previous point is too large, and invalidate the current point. But that would also make you loose not only the connecting line, but also the first point after the jump:

lim=3
y2=y1=0
plot 'test.dat' using (y2=y1,y1=$2,$1):($0 > 0 && abs(y2-y1) > lim ? 1/0 : y1) with linespoints

The test data file I used is

1 1
2 1.1
3 0.95
4 1
5 5
6 6
7 5.5
8 5.8
9 -2
10 -2.5
11 -4

As you see, the points at x=5 and x=9 are lost.

Alternatively, you can pipe your data through an external tool like awk for the filtering. In this case you can insert an empty line when the difference between two consecutive y-values exceeds some limit:

filter(lim) = 'awk ''{if(NR > 1 && sqrt((y-$2)**2) > '.lim.') print ""; print; y=$2}'' test.dat'
plot '< '.filter(3) using 1:2 with lines

Note, that I used the sqrt((..)**2) only to simulate an abs function, which awk doesn't have.