Retrieving weekday name from an integer in a Python dataframe

Question

I would like to convert a column of a dataframe containing weekday integers into its corresponding weekday name. So 0 should become Monday, 1 Tuesday and so forth.

I have tried to convert the integers into a datetime format but it does not work. What is the best way to go about it?

data = {'weekday_number': [1, 2, 0, 3, 4, 5, 6, 3, 2, 5, 4, 5]}
df = pd.DataFrame(data)

df['weekday_name'] = pd.to_datetime(df['weekday_number']).dt.strftime('%A')

Answer 1

Use map for that. First, create a dictionary for mapping days with their numbers

days = {0:'Monday', 1:'Tuesday', 2:'Wednesday', 3:'Thursday', 4:'Friday', 5:'Saturday', 6:'Sunday'}

then

df['weekday_name'] = df['weekday_number'].map(days)

Answer 2

You can use date objects to do the conversion, by using your weekday number as a timedelta from a date which is a Monday:

import pandas as pd
from datetime import date, timedelta

data = {'weekday_number': [1, 2, 0, 3, 4, 5, 6, 3, 2, 5, 4, 5]}
df = pd.DataFrame(data)

df['weekday_name'] = df['weekday_number'].apply(lambda w:(date(2021, 2, 1) + timedelta(days = w)).strftime('%A'))

print(df)

Output

    weekday_number weekday_name
0                1      Tuesday
1                2    Wednesday
2                0       Monday
3                3     Thursday
4                4       Friday
5                5     Saturday
6                6       Sunday
7                3     Thursday
8                2    Wednesday
9                5     Saturday
10               4       Friday
11               5     Saturday

You can also use the day_name array from calendar :

from calendar import day_name

df['weekday_name'] = df['weekday_number'].apply(lambda w:day_name[w])

Or using map with day_name , converting the array into a dict:

df['weekday_name'] = df['weekday_number'].map(dict(enumerate(day_name)))

The results are the same as shown above.

Answer 3

Without a library, you would be best of programming it on a case-by-case basis:

for i in range(len(array)):
    if(array[i] == 0):
        array[i] = "Monday"
    elif(array[i] == 1):
        array[i] = "Tuesday"
    ...

You can also use the calendar module.

import calendar
for i in range(len(array)):
    array[i] = calendar.day_name[array[i]]