Extracting rows/columns of numbers from a txt file in Python

Question

I am fairly new to Python and have encountered a small but (what seems to be a) very difficult problem.

I have a txt file which contains the following:

-2      2.1     -0.365635756
0       2.4      0.347433737
2       2.5      0.263774619
4       3.5     -0.244930974
6       4.2     -0.004564913

My aim is to somehow extract separate rows/columns from the file in Python to use as lists or arrays (again, I'm fairly new to this). So for example, how would I make the list [-2, 0, 2, 4, 6] using the data from the first column?

I currently have the following code in my work:

import numpy as np

with open('Numbers.txt', 'r') as f:
    fcontents = f.read()
    print(fcontents)

x = np.array(fcontents)

The objective of this is to write a program that uses arrays to calculate different variables given in our project instructions.

Use the space character as a delimiter in every line of the text file — Jeru Luke
– Jeru Luke, Commented Apr 19, 2017 at 20:21
Possible duplicate of How to Convert a Text File into a List in Python — Barney
– Barney, Commented Apr 19, 2017 at 20:37

Robᵩ · Accepted Answer · 2017-04-19 20:58:15Z

1

This might be a job for pandas:

import pandas as pd

df = pd.read_fwf('Numbers.txt', header=None)
first_col = df[0]

assert first_col.mean() == 2
assert first_col.median() == 2
assert sum(first_col) == 10

References:

edited Apr 19, 2017 at 20:58

answered Apr 19, 2017 at 20:28

Robᵩ

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1 Comment

MaxU - stand with Ukraine Over a year ago

Yay! Pandas rules! But for this particular file format i'd use pd.read_fwf()

davidejones · Accepted Answer · 2017-04-19 20:26:09Z

0

I haven't used numpy but if you want to separate into columns you can do this kind of thing

col1 = []
col2 = []
col3 = []

with open('Numbers.txt', 'r') as f:
    for line in f:
        first, second, third = line.split()
        col1.append(first)
        col2.append(second)
        col3.append(third)

print(col1)
print(col2)
print(col3)

which outputs

['-2', '0', '2', '4', '6']
['2.1', '2.4', '2.5', '3.5', '4.2']
['-0.365635756', '0.347433737', '0.263774619', '-0.244930974', '-0.004564913']

answered Apr 19, 2017 at 20:26

davidejones

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Comments

Luchko · Accepted Answer · 2017-04-19 21:16:15Z

0

You can import your data as a numpy.array

import numpy as np

data = np.genfromtxt('Numbers.txt', unpack=True).T

Then, retrieving columns/rows is as simple as indexing/slicing a numpy.array

print(data[1,:])
print(data[:,1])

this will results in

[ 0.          2.4         0.34743374]
[ 2.1  2.4  2.5  3.5  4.2]

edited Apr 19, 2017 at 21:16

answered Apr 19, 2017 at 21:06

Luchko

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