How can I merge columns `Year`, `Month`, and `Day` into one column of months?-CodePudding

How can I merge columns Year, Month, and Day into one column of months?

import pandas as pd
data = {'Subject': ['A', 'B', 'C', 'D'],
        'Year':[1, 0, 0, 2],
        'Month':[5,2,8,8],
       'Day': [3,22,5,12]}
df = pd.DataFrame(data)
print(df)

My example gives the resulting dataframe:

  Subject  Year  Month  Day
0       A     1      5    3
1       B     0      2   22
2       C     0      8    5
3       D     2      8   12

I would like it to look like this:
*note: I rounded this so these numbers are not 100% accurate

  Subject  Months
0       A     17
1       B     3
2       C     8
3       D     32

CodePudding user response：

Assuming the Gregorian calendar:

365.2425 days/year
30.436875 days/month.

day_year = 365.2425
day_month = 30.436875

df['Days'] = df.Year.mul(day_year)   df.Month.mul(day_month)   df.Day
# You could also skip this step and just do:
# df['Months'] = (df.Year.mul(day_year)   df.Month.mul(day_month)   df.Day).div(day_month)
df['Months'] = df.Days.div(day_month)
print(df.round(2))

Output:

  Subject  Year  Month  Day    Days  Months
0       A     1      5    3  520.43   17.10
1       B     0      2   22   82.87    2.72
2       C     0      8    5  248.50    8.16
3       D     2      8   12  985.98   32.39