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Pandas – Check if Date is the First Day of a Month

The datetime type in pandas comes with a number of useful built-in functions to get additional information about the given date. In this tutorial, we will look at how to check if a date in a pandas dataframe is the first day of a month or not with the help of some examples.

Using the is_month_start attribute

check if a date is the first day of a month in pandas

You can use is_month_start attribute on a pandas series (or a column in a dataframe) containing datetime values with the help the .dt accessor to check if each date is the start date of a month or not.

The following is the syntax –

df["Date"].dt.is_month_start

It returns a boolean pandas series where True represents that the corresponding date is the first date of the month and False represents that it’s not.

Examples

Let’s now look at some examples of using the above syntax.

First, we will create a sample dataframe to apply the above method.

import pandas as pd

# create a dataframe
df = pd.DataFrame({
    "Date": pd.date_range("2023-03-01", "2023-03-10"),
    "Sales": [10, 12, 7, 17, 21, 5, 11, 13, 14, 8]
})

# display the dataframe
df

Output:

the resulting pandas dataframe with date level sales data

Here, we created a dataframe with the sales data for an ecommerce website for the first 10 days of March 2023. Notice, we used the pandas date_range() function to get datetime values from “2023-03-01” to “2023-03-10” (both inclusive).

Let’s now check whether the dates in the “Date” represent the first day of a month or not.

df["Date"].dt.is_month_start

Output:

0     True
1    False
2    False
3    False
4    False
5    False
6    False
7    False
8    False
9    False
Name: Date, dtype: bool

We get a pandas series of boolean values.

Let’s add the result from the is_month_start attribute as an additional column in the above dataframe.

# add new column
df["Is First Day of Month"] = df["Date"].dt.is_month_start
# display the dataframe
df

Output:

dataframe with new column "Is First Day of Month" added

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Author

  • Piyush

    Piyush is a data scientist passionate about using data to understand things better and make informed decisions. In the past, he's worked as a Data Scientist for ZS and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects.