Creating lists from a text file by splitting it vertically

Question

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 1

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

Answer 2

You can use the csv lib:

import csv

x, y, e = [], [], []
with open("in.csv") as f:
    next(f)
 for a, b, c in csv.reader(f, delimiter=" ", skipinitialspace=1):
    x.append(float(a))
    y.append(float(b))
    e.append(float(c))

Output:

[-2.0, 0.0, 2.0, 4.0, 6.0]
[2.1, 2.4, 2.5, 3.5, 4.2]
[0.170358869161, 0.170202773308, -0.138557648063, 0.187965696415, -0.473073365465]

Or using with a defaultdict to group the elements:

import csv
from collections import defaultdict


with open("in.csv") as f:
    d = defaultdict(list)
    for dct in csv.DictReader(f, delimiter=" ", skipinitialspace=1):
        for k, v in dct.items():
            d[k].append(float(v))

from pprint import  pprint as pp

pp(dict(d))

Output:

{'e': [0.170358869161,
       0.170202773308,
       -0.138557648063,
       0.187965696415,
       -0.473073365465],
 'x': [-2.0, 0.0, 2.0, 4.0, 6.0],
 'y': [2.1, 2.4, 2.5, 3.5, 4.2]}

Answer 3

I see that the replies above have answers that used hard-coded variables. However I found a way to create lists that can hold infinite lines.

def getFrom(index: int, data: list):
    returnList = []
    for item in data:
        if len(item) >= index:
            returnList.append(item[index])
        else:
            returnList.append("")
    return returnList

In this function, data is the list that you want to search, can be nested, while index is the index you wanted to search. This will return a list contains that was in the index on the vertical space.

You can also try

data = ...
endList = [getFrom(index, data) for index in range(len(data))]

and endList if the result of the array split vertically.