Reading specific columns from a text file in python

Question

I have a text file which contains a table comprised of numbers e g   5 10 6 6 20 1 7 30 4 8 40 3 9 23 1 4 13 6  if for example I want the numbers contained only in the second column  how do i extract that column into a list

User · Accepted Answer

f open file  quot r quot   lines f readlines   result    for x in lines      result append x split      1   f close    You can do the same using a list comprehension print  x split      1  for x in open file  readlines      Docs on split    string split s   sep   maxsplit    Return a list of the words of the string s  If the optional second argument sep is absent or None  the words are separated by arbitrary strings of whitespace characters  space  tab  newline  return  formfeed   If the second argument sep is present and not None  it specifies a string to be used as the word separator  The returned list will then have one more item than the number of non-overlapping occurrences of the separator in the string   So  you can omit the space I used and do just x split   but this will also remove tabs and newlines  be aware of that

User · Answer

You have a space delimited file  so use the module designed for reading delimited values files  csv   import csv  with open  path to file txt   as inf      reader   csv reader inf  delimiter          second col   list zip  reader   1        In Python2  you can omit the  list       cast   The zip  iterable  pattern is useful for converting rows to columns or vice versa  If you re reading a file row-wise      gt  gt  gt  testdata     1  2  3                    4  5  6                    7  8  9     gt  gt  gt  for line in testdata          print line    1  2  3   4  5  6   7  8  9       but need columns  you can pass each row to the zip function   gt  gt  gt  testdata columns   zip  testdata    this is equivalent to zip  1 2 3    4 5 6    7 8 9     gt  gt  gt  for line in testdata columns          print line    1  4  7   2  5  8   3  6  9

User · Answer

First of all we open the file and as datafile then we apply  read   method reads the file contents and then we split the data which returns something like    5    10    6    6    20    1    7    30    4    8    40    3    9    23    1    4    13    6   and the we applied list slicing on this list to start from the element at index position 1 and skip next 3 elements untill it hits the end of the loop   with open  sample txt    r   as datafile      print datafile read   split   1  3    Output     10    20    30    40    23    13

User · Answer

It may help   import csv with open  csv file   r   as f        Printing Specific Part of CSV file       Printing last line of second column     lines   list csv reader f  delimiter        skipinitialspace   True       print lines -1  1         For printing a range of rows except 10 last rows of second column     for i in range len lines -10           print lines i  1

User · Answer

I know this is an old question  but nobody mentioned that when your data looks like an array  numpy s loadtxt comes in handy    gt  gt  gt  import numpy as np  gt  gt  gt  np loadtxt  myfile txt      1  array  10   20   30   40   23   13

User · Answer

You can use a zip function with a list comprehension    with open  ex txt   as f      print zip   line split   for line in f   1    result      10    20    30    40    23    13

[python] Reading specific columns from a text file in python

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