How to convert column data from text file into list in Python?

Question

I have a text file that contains data in two columns, each of which I want to read into Python as a list.

For example :

       2500.3410      -0.60960758
       2505.5803       -1.3031826
       2510.8197      -0.64067196
       2516.0593       -1.0230898
       2521.2991      -0.20078891

I want to create two lists, one containing the data from column 1 and the other column 2, but I don't know how to tell Python to do this.

E.g.

list1 = [2500.3410, 2505.5803, 2510.8197, 2516.0593, 2521.2991]

I have opened the file in the shell and can read in the data, as above, but I'm stuck when it comes to creating the lists.

Anupam · Accepted Answer · 2015-03-22 19:32:13Z

1

First of all you have to read the text file in Python , for an instance if you have a file named record.txt containg dataset,

file <- open('record.txt')

now you have to read the file line by line :

lst = []

stores the whole file as a list of list and each inner list represents an instance

for line in file:
    lst.append([ float(x) for x in line.split()])

now you can extract the column1 as a list and column 2 as a list by following comprehension

column1 = [ x[0] for x in lst]
column2 = [ x[1] for x in lst]

answered Mar 22, 2015 at 19:32

Anupam

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Comments

Kasravnd · Accepted Answer · 2015-03-22 19:11:41Z

You can use zip function and float within map :

zip(*[map(float,line.split()) for line in open('in_file')])

Demo:

>>> s="""       2500.3410      -0.60960758
...        2505.5803       -1.3031826
...        2510.8197      -0.64067196
...        2516.0593       -1.0230898
...        2521.2991      -0.20078891"""
>>> 
>>> [i.split() for i in s.split('\n')]
[['2500.3410', '-0.60960758'], ['2505.5803', '-1.3031826'], ['2510.8197', '-0.64067196'], ['2516.0593', '-1.0230898'], ['2521.2991', '-0.20078891']]
>>> zip(*[map(float,i.split()) for i in s.split('\n')])
[(2500.341, 2505.5803, 2510.8197, 2516.0593, 2521.2991), (-0.60960758, -1.3031826, -0.64067196, -1.0230898, -0.20078891)]

But note as zip return a list of tuples you can use map function to convert the result to list :

>>> map(list,zip(*[map(float,i.split()) for i in s.split('\n')]))
[[2500.341, 2505.5803, 2510.8197, 2516.0593, 2521.2991], [-0.60960758, -1.3031826, -0.64067196, -1.0230898, -0.20078891]]

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