How to Merge DataFrames of different length in Pandas ?

In this article, we will discuss how to merge the two dataframes with different lengths in Pandas. It can be done using the merge() method.

Syntax:

DataFrame.merge(parameters)

Below are some examples that depict how to merge data frames of different lengths using the above method:

Example 1:

Below is a program to merge two student data frames of different lengths.

Python3

# importing pandas module

import pandas as pd

# create a list that contains
# student id of subject 1
list1 = [7058, 7059, 7075, 7076]

# create a list that contains
# student id of subject 2
list2 = [7058, 7059, 7012, 7075, 7076]

# create a list that contains
# student names of subject 1
list11 = ["Sravan", "Jyothika", "Deepika",
          "Kyathi"]

# create a list that contains
# student names of subject 2
list22 = ["Sravan", "Jyothika", "Salma",
          "Deepika", "Kyathi"]


# pass list1 and list11 to the
# dataframe1
dataframe1 = pd.DataFrame(
  {"Student ID": list1, "Student Name": list11})
print('First data frame:')
display(dataframe1)

# pass list2 and list22 to the
# dataframe1
dataframe2 = pd.DataFrame(
  {"Student ID": list2, "Student Name": list22})
print('Second data frame:')
display(dataframe2)

# apply merge function to merge the
# two dataframes
mergedf = dataframe2.merge(dataframe1, how='left')
print('Merged data frame:')
display(mergedf)

Output:

Example 2:

Here is another program to merge one data frame of length 4 and another dataframe of length 9.

Python3

# importing pandas module
import pandas as pd

# create a list that contains
# student id of subject 1
list1 = [7058, 7059, 7075, 7076]

# create a list that contains
# student id of subject 2
list2 = [7058, 7059, 7012, 7075, 7076,
         7034, 7046, 7036, 7015]

# create a list that contains
# student names of subject 1
list11 = ["Sravan", "Jyothika", "Deepika",
          "Kyathi"]

# create a list that contains
# student names of subject 2
list22 = ["Sravan", "Jyothika", "salma",
          "Deepika", "Kyathi", "meghana",
          "pranathi", "bhanu", "keshav"]


# pass list1 and list11 to the
# dataframe1
dataframe1 = pd.DataFrame(
  {"Student ID": list1, "Student Name": list11})
print('First data frame:')
display(dataframe1)

# pass list2 and list22 to the
# dataframe1
dataframe2 = pd.DataFrame(
  {"Student ID": list2, "Student Name": list22})
print('Second data frame:')
display(dataframe2)

# apply merge function to merge
# the two dataframes
mergedf = dataframe2.merge(dataframe1, how='inner')
print('Merged data frame:')
display(mergedf)

Output: