reading a text file columnwise and storing in a list in python

Question

I have a text file in the following format:

a,b,c,d,
1,1,2,3,
4,5,6,7,
1,2,5,7,
6,9,8,5,

How can i read it into a list efficiently so as to get the following output?

list=[[1,4,1,6],[1,5,2,9],[2,6,5,8],[3,7,7,5]]

Answer 1

Let's assume that the file is named spam.txt :

$ cat spam.txt
a,b,c,d,
1,1,2,3,
4,5,6,7,
1,2,5,7,
6,9,8,5,    

Using list comprehensions and the zip() built-in function, you can write a program such as:

>>> with open('spam.txt', 'r') as file:
...     file.readline() # skip the first line
...     rows = [[int(x) for x in line.split(',')[:-1]] for line in file]
...     cols = [list(col) for col in zip(*rows)]
... 
'a,b,c,d,\n'
>>> rows
[[1, 1, 2, 3], [4, 5, 6, 7], [1, 2, 5, 7], [6, 9, 8, 5]]
>>> cols
[[1, 4, 1, 6], [1, 5, 2, 9], [2, 6, 5, 8], [3, 7, 7, 5]]

Additionally, zip(*rows) is based on unpacking argument lists , which unpacks a list or tuple so that its elements can be passed as separate positional arguments to a function. In other words, zip(*rows) is reduced to zip([1, 1, 2, 3], [4, 5, 6, 7], [1, 2, 5, 7], [6, 9, 8, 5]) .

EDIT:

This is a version based on NumPy for reference:

>>> import numpy as np
>>> with open('spam.txt', 'r') as file:
...     ncols = len(file.readline().split(',')) - 1
...     data = np.fromiter((int(v) for line in file for v in line.split(',')[:-1]), int, count=-1)
...     cols = data.reshape(data.size / ncols, ncols).transpose()
...
>>> cols
array([[1, 4, 1, 6],
       [1, 5, 2, 9],
       [2, 6, 5, 8],
       [3, 7, 7, 5]])

Answer 2

You can try the following code:

from numpy import*

x0 = []
for line in file('yourfile.txt'):
    line = line.split()
    x = line[1]
   x0.append(x)

for i in range(len(x0)):
print x0[i]

Here the first column is appended onto x0[]. You can append the other columns in a similar fashion.

Answer 3

You can use data_py package to read column wise data from a file. Install this package by using

pip install data-py==0.0.1

Example

from data_py import datafile
df1=datafile("C:/Folder/SubFolder/data-file-name.txt")
df1.separator=","
[Col1,Col2,Col3,Col4,Col5]=["","","","",""]
[Col1,Col2,Col3,Col4,Col5]=df1.read([Col1,Col2,Col3,Col4,Col5],lineNumber)
print(Col1,Col2,Col3,Col4,Col5)

For details please follow the link https://www.respt.in/p/python-package-datapy.html