Python CSV module, add column to the side, not the bottom

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November 29th, 2012, 10:21 PM

ufloridagator

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Python CSV module, add column to the side, not the bottom

I am new in python, and I need some help. I made a python script that takes two columns from a file and copy them into a "new file". However, every now and then I need to add columns to the "new file". I need to add the columns on the side, not the bottom. My script adds them to the bottom. Someone suggested using CSV, and I read about it, but I can't make it in a way that it adds the new column to the side of the previous columns. Any help is highly appreciated.

Here is the code that I wrote.

import sys
import re

filetoread = sys.argv[1]
filetowrite = sys.argv[2]

newfile = str(filetowrite) + ".txt"

openold = open(filetoread,"r")
opennew = open(newfile,"a")

rline = openold.readlines()

number = int(len(rline))
start = 0

for i in range (len(rline)) :
if "2theta" in rline[i] :
start = i

for line in rline[start + 1 : number] :
words = line.split()
word1 = words[1]
word2 = words[2]
opennew.write (word1 + " " + word2 + "\n")

openold.close()
opennew.close()

here is the second code I wrote using CSV

import sys
import re
import csv

filetoread = sys.argv[1]
filetowrite = sys.argv[2]

newfile = str(filetowrite) + ".txt"

openold = open(filetoread,"r")

rline = openold.readlines()

number = int(len(rline))
start = 0

for i in range (len(rline)) :
if "2theta" in rline[i] :
start = i

words1 = []
words2 = []

for line in rline[start + 1 : number] :
words = line.split()
word1 = words[1]
word2 = words[2]
words1.append([word1])
words2.append([word2])

with open(newfile, 'wb') as file:
writer = csv.writer(file, delimiter= "\n")
writer.writerow(words1)
writer.writerow(words2)

My first script works "almost" great, except that it writes the new columns at the bottom and I need them at side of the previous columns.

November 30th, 2012, 03:22 PM

b49P23TIvg

Contributing User

Join Date: Aug 2011

Posts: 3,357

Time spent in forums: 1 Month 2 Weeks 3 Days 9 h 22 m 15 sec
Reputation Power: 383

Use executable Iverson notation, J instead of python.

Code:

   [A=: i. 4 5   NB. make an array  A
 0  1  2  3  4
 5  6  7  8  9
10 11 12 13 14
15 16 17 18 19
   

   [B=: 100 + i. 4 _3   NB. another array, B
102 101 100
105 104 103
108 107 106
111 110 109
   

   A , B       NB. concatenated with default fill 0
  0   1   2  3  4
  5   6   7  8  9
 10  11  12 13 14
 15  16  17 18 19
102 101 100  0  0
105 104 103  0  0
108 107 106  0  0
111 110 109  0  0
   

   A ,. B    NB. stitched
 0  1  2  3  4 102 101 100
 5  6  7  8  9 105 104 103
10 11 12 13 14 108 107 106
15 16 17 18 19 111 110 109

Oh well, this is a python forum. Your program needs to read the data with the lines to which you want to append data. And then you need to rewrite the entire file argv[2]. Also there's a good chance I didn't understand your intent.

command line

Code:

$ python p.py a b

Quote:

Originally Posted by a input

2theta
a b c d e f
g h i j

Quote:

Originally Posted by b.txt input

I have the same row count as the other file
has lines following the line with '2theta'.

Quote:

Originally Posted by b.txt output

I have the same row count as the other file b c
has lines following the line with '2theta'. h i

Quote:

Originally Posted by b.txt.bak output

I have the same row count as the other file
has lines following the line with '2theta'.

program

Code:

# the link at my signature is supposed to explain how to post python

import sys
import os

filetoread = sys.argv[1]
filetowrite = sys.argv[2]

newfile = str(filetowrite) + ".txt"

with open(filetoread,"r") as openold:     # context closes the file
    rline = openold.readlines()

start = 0
for (i,Line,) in enumerate(rline):        # enumerate function easier
    if "2theta" in rline[i] :
        start = i
        break

# read the "newfile".  You need the lines to append data.
with open(newfile,'r') as inf:
    change_these_rows = inf.readlines()

for (i,L,) in enumerate(change_these_rows):
    # insertion is a list of words 1 and 2
    insertion = rline[start+1+i].split()[1:3]
    # remove the line end from the row, make a list of the 3 pieces, join them with space, and attach a new line end character.
    change_these_rows[i] = ' '.join([L[:-1]]+insertion)+'\n'

# make a backup file!
print('delete 1/0 if writing a new file is ok')
1/0
os.rename(newfile,newfile+'.bak')

with open(newfile,'w') as ouf:           # again, use the file context
    ouf.writelines(change_these_rows)

__________________
[code]Code tags[/code] are essential for python code!

Last edited by b49P23TIvg : November 30th, 2012 at 03:24 PM.

December 1st, 2012, 03:09 PM

ufloridagator

Registered User

Join Date: Nov 2012

Posts: 8

Time spent in forums: 1 h 4 m 10 sec
Reputation Power: 0

I am getting this error with the code you suggested me.

Traceback (most recent call last):
File "paula9.py", line 27, in <module>
insertion = rline[(start+1)+i].split()[1:3]
IndexError: list index out of range

December 1st, 2012, 03:46 PM

b49P23TIvg

Contributing User

Join Date: Aug 2011

Posts: 3,357

Time spent in forums: 1 Month 2 Weeks 3 Days 9 h 22 m 15 sec
Reputation Power: 383

2theta needed to appear,
and you needed to know that LIST[0] is the first object in the list, and I didn't incorporate error tests for bad input.

Python CSV module, add column to the side, not the bottom

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