Skip specific data lines from a .txt file in order to plot a 2D line with breaks

Question

I am trying to plot a graph with one plot only regarding certain lines of its textfile.

How can I achieve this in my py script?

import pylab as py
xa, ya = py.loadtxt('filename1.txt',skiprows=1,usecols=(0,1),unpack=True ) 
xb, yb = py.loadtxt('filename2.txt',skiprows=1,usecols=(0,1),unpack=True )

fig = py.figure(1,figsize=(12,14))

py.semilogy(xa, ya*2, '-', xb, yb*1.5, 'o', linewidth = 0.5) 

My textfiles have 100 rows (and 2 columns) and I want to skip the lines 35:55 and 65:77 of 'filename2.txt' in order to plot a 2d line with gaps in between. Unfortunately I can't find a solution for this simple task via matplotlib.

Answer 1

If your data is not so big it might be easier to read all and then just select the required indices from your data:

idx = np.arange(xb.shape[0])   # array([0, 1, 2, 3, 4, 5, 6, ...
mask = (idx < 35) | (idx > 55) | (idx < 65) | (idx > 77)
xb, yb = xb[mask], yb[mask]

Answer 2

You can just set the unwanted datapoints in ya and yb to np.nan. Matplot skips (or just doesn't plot) those points.

So you could do (after reading the txt file):

np.put(ya,range(35,56,1),[np.nan]*(56-35))

and so on for the other parts. xa and xb should stay as they are.