jlt jlt - 7 months ago 19
Python Question

Creating lists from a text file by splitting it vertically

I want to split this text file into 3 (called

x
,
y
, and
e
) lists using Python and I can't seem to do it.

This is what the text file (called data) looks like:

x y e
-2 2.1 0.170358869161
0 2.4 0.170202773308
2 2.5 -0.138557648063
4 3.5 0.187965696415
6 4.2 -0.473073365465


This is the code I have so far that doesn't work:

x=[]
y=[]
e=[]

try:
data = open('data.txt', 'rt')
except:
sys.exit('cannot find file')

with data:
try:
x.append(data[:1])
y.append(data[2:3])
e.append(data[4:5])
except:
sys.exit('cannot create lists')

Answer

Do this:

with data as f:     # f is the file object
    for line in f:  # you can iterate over a file object line-by-line
        xi, yi, ei = line.split()
        x.append(xi)
        y.append(yi)
        e.append(ei.strip()) # ei will have a \n on the end

You can coerce them to ints or floats when appending them, if your assumptions about their shape are correct.

If you have pandas, I recommend read_csv:

>>> import pandas as pd
>>> pd.read_csv('data.txt', delim_whitespace=True)
   x    y         e
0 -2  2.1  0.170359
1  0  2.4  0.170203
2  2  2.5 -0.138558
3  4  3.5  0.187966
4  6  4.2 -0.473073