How to create a datetime column from year, month and day columns in pandas ?

Examples of how to create a datetime column from year, month and day columns in pandas:

Table of contents

Create a dataframe
Create a datetime column
Set datetime column as the dataframe index
References

Create a dataframe

Let's first create a dataframe in pandas with 3 columns "Year", "Month" and "Day":

import pandas as pd
import random
import itertools

year_list = []
month_list = []
day_list = []

for combination in itertools.product([2015], [1,2,3,4], [5,15,25]):
        #print(combination) 
        year_list.append( combination[0] )
        month_list.append( combination[1] )
        day_list.append( combination[2] )

data = {'Year':year_list,
                'Month':month_list,
                'Day':day_list,
                'Random Integer':[random.randrange(1, 10) for i in range(len(year_list))]}

df = pd.DataFrame(data=data)

print(df)

returns for example

            Year  Month  Day  Random Integer
0   2015      1    5               7
1   2015      1   15               5
2   2015      1   25               6
3   2015      2    5               4
4   2015      2   15               1
5   2015      2   25               2
6   2015      3    5               4
7   2015      3   15               9
8   2015      3   25               3
9   2015      4    5               1
10  2015      4   15               3
11  2015      4   25               7

Create a datetime column

To create a new datetime column using 'Year', 'Month' and 'Day' columns, a solution is to use to_datetime():

df['Datetime'] = pd.to_datetime( df[['Year', 'Month', 'Day']])

returns

        Year  Month  Day  Random Integer   Datetime
0   2015      1    5               7 2015-01-05
1   2015      1   15               5 2015-01-15
2   2015      1   25               6 2015-01-25
3   2015      2    5               4 2015-02-05
4   2015      2   15               1 2015-02-15
5   2015      2   25               2 2015-02-25
6   2015      3    5               4 2015-03-05
7   2015      3   15               9 2015-03-15
8   2015      3   25               3 2015-03-25
9   2015      4    5               1 2015-04-05
10  2015      4   15               3 2015-04-15
11  2015      4   25               7 2015-04-25

Set datetime column as the dataframe index

Now, if you want to set the datetime column as the dataframe index,a solution is to use set_index():

df.set_index('Datetime', inplace=True)

returns

                     Year  Month  Day  Random Integer
Datetime                                    
2015-01-05  2015      1    5               7
2015-01-15  2015      1   15               5
2015-01-25  2015      1   25               6
2015-02-05  2015      2    5               4
2015-02-15  2015      2   15               1
2015-02-25  2015      2   25               2
2015-03-05  2015      3    5               4
2015-03-15  2015      3   15               9
2015-03-25  2015      3   25               3
2015-04-05  2015      4    5               1
2015-04-15  2015      4   15               3
2015-04-25  2015      4   25               7

Can be used to plot a time series:

How to create a datetime column from year, month and day columns in pandas ?

Note to reset the index:

df.reset_index(inplace=True)

References

Developer in my spare time, I’m interested in Earth observation and satellite-based fire detection. Passionate about Python, machine learning, and open science.

How to create a datetime column from year, month and day columns in pandas ?

Create a dataframe

Create a datetime column

Set datetime column as the dataframe index

References

Benjamin

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