Plot 2D, from a 3D file that contains blocked data every time x changes.

[David]

I have a data.dat file that looks like:

# z      y      x
25.04   12.50  10.00
24.01   11.30  10.00
25.03   12.50  10.00
22.01   14.20  10.00

27.05   14.28  20.00
28.01   12.30  20.00
27.70   13.37  20.00
27.10   14.08  20.00

30.20   16.22  30.00
31.22   17.01  30.00
32.01   17.02  30.00
32.44   16.32  30.00
.
.
.

Following the instructions posted on section 3.9 of FAQ, I
I generated that file intentionally with a blank space every time the x value changes, in order to achieve a final splot of z as a function of x and y.

Now, in the same gnuplot script, I would need to plot 2D graphs in which:

I plot the variation of z as a function of y for different values of x.

Is there a way to do this on gnuplot on the same script ?