如何使用Python在同一文件中将一列除以另一列？

Question

I have a very long file.txt that exceeds 1000000 rows, contains two columns as follows:

photon  electron
1000     100
1010     122
2000     50
1520     190
....     ....

I want a 3rd column as division: electron / photon how can it possible in Python?

Answer 1

One option using pandas :

import pandas as pd

with open('file.txt', 'r') as f:
    df = pd.read_csv(f, sep='\s+', header=0)

df['e/p'] = df['electron'] / df['photon']

print(df)

result:

   photon  electron       e/p
0    1000       100  0.100000
1    1010       122  0.120792
2    2000        50  0.025000
3    1520       190  0.125000

Same result without pandas , using standard-library:

import csv

d = []
with open('file.txt', 'r') as f:
    data = list(csv.reader(f, delimiter=' ', skipinitialspace=True))
    d += [data[0]]
    d[0].append('e/p')
    for l in list(data)[1::]:
        l.append(round(float(l[1])/float(l[0]), 6))
        d.append(l)

for i in d:
    print '{:<9} {:<9} {:<9}'.format(*i)

result:

photon    electron  e/p      
1000      100       0.1      
1010      122       0.120792 
2000      50        0.025    
1520      190       0.125 

Format as desired for python2 or python3.