How to Append Two Pandas DataFrames

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  • Post category:Pandas
  • Post last modified:May 23, 2024
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You are currently viewing How to Append Two Pandas DataFrames

To append two Pandas DataFrames, you can use the append() function. There are multiple ways to append two pandas DataFrames, In this article, I will explain how to append two or more pandas DataFrames by using several functions.

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In order to append two DataFrames you can use DataFrame.append() function. When you are appending two or more DataFrames, pass all DataFrames as a list to this method.

Key Points –

  • Use the append() function to concatenate two DataFrames vertically, adding rows from one DataFrame to the end of the other.
  • Specify the ignore_index=True parameter to reset the index of the resulting DataFrame after appending, ensuring a continuous index.
  • Consider alternatives such as pd.concat() for more complex concatenation operations or DataFrame.append() for appending a single row or column.

Quick Examples of Appending

Below are some quick examples of appending two DataFrames in pandas.


# Quick examples of append two dataframes

# Append two DataFrames of same column
df3 = df1.append(df2)

# Append two DataFrames of different columns
df2 = df.append(df1)

# Using append() with ignore_index
df2 = df.append(df1, ignore_index=True)

# Appending three DataFrames
df3 = df.append([df1, df2], ignore_index=True)

Create Two Append DataFrames

To run some examples of appending two pandas DataFrames, let’s create DataFrame using data from a dictionary.


# Create two DataFrames with same columns
import pandas as pd

df1 = pd.DataFrame({'Courses': ["Spark","PySpark","Python","pandas"],
                    'Fee' : [20000,25000,22000,24000]})
print("First DataFrame:\n", df1)

df2 = pd.DataFrame({'Courses': ["Pandas","Hadoop","Hyperion","Java"],
                    'Fee': [25000,25200,24500,24900],
                    'Duration': ['30days','35days','40days','45days']})
print("Second DataFrame:\n", df2)

Yields below output.

pandas append two DataFrames

To append two DataFrames with the same columns in Pandas, you can utilize the append() function. This function concatenates the DataFrames along the specified axis, filling in NaN values for rows where columns don’t match.


# Append two DataFrames of same columns
# using append() function
df3 = df1.append(df2)
print("After appending DataFrames:\n", df3)

Yields below output.

pandas append two DataFrames

Append Two DataFrames With the Different Columns

Alternatively, to append two pandas DataFrames with different columns, we can utilize the append() method. This method allows you to combine DataFrames along a specified axis (rows or columns), and it handles the alignment of columns with different names.


# Craete DataFrames of different columns
import pandas as pd
df1 = pd.DataFrame({'Courses': ["Spark","PySpark","Python","pandas"],
                    'Fee' : [20000,25000,22000,24000]})
print("First DataFrame:\n", df1)

df2 = pd.DataFrame({'discount': [2500,2520,2450,2490],
                    'Duration': ['30days','35days','40days','45days']})
print("Second DataFrame:\n", df2)

# Append two DataFrames of different columns
# using append() function
df3 = df1.append(df2)
print("After appending DataFrames:\n", df3)

Yields below output.


# Output:
First DataFrame:
    Courses    Fee
0    Spark  20000
1  PySpark  25000
2   Python  22000
3   pandas  24000
Second DataFrame:
    discount Duration
0      2500   30days
1      2520   35days
2      2450   40days
3      2490   45days

After appending DataFrames:
    Courses      Fee  discount Duration
0    Spark  20000.0       NaN      NaN
1  PySpark  25000.0       NaN      NaN
2   Python  22000.0       NaN      NaN
3   pandas  24000.0       NaN      NaN
0      NaN      NaN    2500.0   30days
1      NaN      NaN    2520.0   35days
2      NaN      NaN    2450.0   40days
3      NaN      NaN    2490.0   45days

Append Two DataFrames Ignore Index

To append two Pandas DataFrames while ignoring the index, you can use the ignore_index=True parameter with the append() function. 


# Using append() with ignore_index
df3 = df1.append(df2, ignore_index=True)
print(df3)

Yields below output.


# Output:
   Courses      Fee  discount Duration
0    Spark  20000.0       NaN      NaN
1  PySpark  25000.0       NaN      NaN
2   Python  22000.0       NaN      NaN
3   pandas  24000.0       NaN      NaN
4      NaN      NaN    2500.0   30days
5      NaN      NaN    2520.0   35days
6      NaN      NaN    2450.0   40days
7      NaN      NaN    2490.0   45days

Append Three DataFrames

Similarly, If you have three DataFrames pass all these as a list to the append() method. Using ignore_index=True allows you to reset a DataFrame’s index of a Pandas DataFrame to start from zero.


# Create third DataFrame  
df2 = pd.DataFrame({'Courses':['PHP','GO'],
                    'Duration':['30day','40days'],
                    'Fee':[10000,23000]})
  
# Appending multiple DataFrame
df3 = df.append([df1, df2], ignore_index=True)
print(df3)

Yields below output


# Output:
    Courses    Fee Duration
    Courses    Fee Duration
0     Spark  20000      NaN
1   PySpark  25000      NaN
2    Python  22000      NaN
3    pandas  24000      NaN
4    Pandas  25000   30days
5    Hadoop  25200   35days
6  Hyperion  24500   40days
7      Java  24900   45days
8       PHP  10000    30day
9        GO  23000   40days

Complete Example of Append Two DataFrames


import pandas as pd
# Complete Example of Append Two DataFrames
df = pd.DataFrame({'Courses': ["Spark","PySpark","Python","pandas"],
                    'Fee' : [20000,25000,22000,24000]})

df1 = pd.DataFrame({'Courses': ["Pandas","Hadoop","Hyperion","Java"],
                    'Fee': [25000,25200,24500,24900],
                    'Duration': ['30days','35days','40days','45days']})

# Using append() method
df3 = df1.append(df2)
print(df3)

# Using append() with ignore_index
df3 = df1.append(df2, ignore_index=True)
print(df2)

# Create third DataFrame  
df2 = pd.DataFrame({'Courses':['PHP','GO'],
                    'Duration':['30day','40days'],
                    'Fee':[10000,23000]})
  
# Appending multiple DataFrame
df3 = df.append([df1, df2], ignore_index=True)
print(df3)

FAQ on Append Two DataFrames

How can I combine or append two Pandas DataFrames together?

You can use the append() function in Pandas to concatenate two DataFrames vertically. Simply call the append() method on one DataFrame and pass the other DataFrame as an argument.

Can I reset the index of the appended DataFrame to start from zero?

You can use the ignore_index=True parameter when appending the DataFrames to reset the index of the resulting DataFrame, starting from zero.

Do the DataFrames need to have the same columns to be appended?

The DataFrames do not necessarily need to have the same columns. If they have different columns, the missing columns will be filled with NaN values.

What is the difference between appending DataFrames and merging them in Pandas?

Appending DataFrames (using pd.concat()) stacks DataFrames vertically, combining rows. Merging DataFrames (using pd.merge()) combines DataFrames based on common columns, aligning rows based on common values in those columns.

Conclusion

In this article, I have explained appending two Pandas DataFrames by examples. Also learned how to append even three DataFrame by passing all DF’s you wanted to append as a list.

References