How to Union Pandas DataFrames using Concat

You can union Pandas DataFrames using contact:

pd.concat([df1, df2])

You may concatenate additional DataFrames by adding them within the brackets.

In the next section, you’ll see an example with the steps to union Pandas DataFrames using contact.

Steps to Union Pandas DataFrames using Concat

Step 1: Create the first DataFrame

For example, let’s say that you have the following data about your customers:

clientFirstName	clientLastName	country
Jon	Smith	US
Maria	Lam	Canada
Bruce	Jones	Italy
Lili	Chang	China

You can then create a DataFrame to capture the above data in Python:

import pandas as pd

clients1 = {'clientFirstName': ['Jon','Maria','Bruce','Lili'],
            'clientLastName': ['Smith','Lam','Jones','Chang'],
            'country': ['US','Canada','Italy','China']
           }

df1 = pd.DataFrame(clients1, columns= ['clientFirstName', 'clientLastName','country'])

print (df1)

Run the code in Python and you would get:

Step 2: Create the second DataFrame

Now suppose that you got an additional data about new customers:

clientFirstName	clientLastName	country
Bill	Jackson	UK
Jack	Green	Germany
Elizabeth	Gross	Brazil
Jenny	Sing	Japan

You can then create the second DataFrame as follows:

import pandas as pd

clients2 = {'clientFirstName': ['Bill','Jack','Elizabeth','Jenny'],
            'clientLastName': ['Jackson','Green','Gross','Sing'],
            'country': ['UK','Germany','Brazil','Japan']
           }

df2 = pd.DataFrame(clients2, columns= ['clientFirstName', 'clientLastName','country'])

print (df2)

Run the code, and you’ll see:

Your goal is to union those two DataFrames together. You can then use Pandas concat to accomplish this goal.

Step 3: Union Pandas DataFrames using Concat

Finally, to union the two Pandas DataFrames together, you can apply the generic syntax that you saw at the beginning of this guide:

pd.concat([df1, df2])

And here is the complete Python code to union Pandas DataFrames using concat:

import pandas as pd

clients1 = {'clientFirstName': ['Jon','Maria','Bruce','Lili'],
            'clientLastName': ['Smith','Lam','Jones','Chang'],
            'country': ['US','Canada','Italy','China']
           }

df1 = pd.DataFrame(clients1, columns= ['clientFirstName', 'clientLastName','country'])


clients2 = {'clientFirstName': ['Bill','Jack','Elizabeth','Jenny'],
            'clientLastName': ['Jackson','Green','Gross','Sing'],
            'country': ['UK','Germany','Brazil','Japan']
           }

df2 = pd.DataFrame(clients2, columns= ['clientFirstName', 'clientLastName','country'])

union = pd.concat([df1, df2])
print (union)

Once you run the code, you’ll get the concatenated DataFrames:

Notice that the index values keep repeating themselves (from 0 to 3 for the first DataFrame, and then from 0 to 3 for the second DataFrame):

You may then choose to assign the index values in an incremental manner once you concatenated the two DataFrames.

To do so, simply set ignore_index=True within the pd.concat brackets:

import pandas as pd

clients1 = {'clientFirstName': ['Jon','Maria','Bruce','Lili'],
            'clientLastName': ['Smith','Lam','Jones','Chang'],
            'country': ['US','Canada','Italy','China']
           }

df1 = pd.DataFrame(clients1, columns= ['clientFirstName', 'clientLastName','country'])


clients2 = {'clientFirstName': ['Bill','Jack','Elizabeth','Jenny'],
            'clientLastName': ['Jackson','Green','Gross','Sing'],
            'country': ['UK','Germany','Brazil','Japan']
           }

df2 = pd.DataFrame(clients2, columns= ['clientFirstName', 'clientLastName','country'])

union = pd.concat([df1, df2], ignore_index=True)
print (union)

And the result:

That’s it! The above method that you just saw would work even if you have more than 2 DataFrames. Note that you’ll need to keep the same column names across all the DataFrames to avoid any NaN values.

For additional information about concatenating DataFrames, please visit the Pandas.concat documentation.

You may also want to check the following tutorial that explains how to concatenate column values using Pandas.