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Apply a function to each row or column in Dataframe using pandas.apply()

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  • Difficulty Level : Medium
  • Last Updated : 19 Jul, 2021
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There are different ways to apply a function to each row or column in DataFrame. We will learn about various ways in this post. Let’s create a small dataframe first and see that. 

Python3




# import pandas and numpy library
import pandas as pd
import numpy as np
  
# list of tuples
matrix = [(1,2,3,4),
          (5,6,7,8,),
          (9,10,11,12),
          (13,14,15,16)
         ]
  
# Create a Dataframe object
df = pd.DataFrame(matrix, columns = list('abcd'))
  
# Output
df

Output : 
 

dataframe

Method 1: Applying lambda function to each row/column. 
Example 1: For Column 

Python3




# import pandas and numpy library
import pandas as pd
import numpy as np
 
# list of tuples
matrix = [(1,2,3,4),
          (5,6,7,8,),
          (9,10,11,12),
          (13,14,15,16)
         ]
 
# Create a Dataframe object
df = pd.DataFrame(matrix, columns = list('abcd'))
 
# Applying a lambda function to each
# column which will add 10 to the value
new_df = df.apply(lambda x : x + 10)
 
# Output
new_df

Output : 

 

dataframe-apply function-1

 

Example 2: For Row 

Python3




# import pandas and numpy library
import pandas as pd
import numpy as np
 
# list of tuples
matrix = [(1,2,3,4),
          (5,6,7,8,),
          (9,10,11,12),
          (13,14,15,16)
         ]
 
# Creating a Dataframe object
df = pd.DataFrame(matrix, columns = list('abcd'))
 
# Applying a lambda function to each
# row which will add 5 to the value
new_df = df.apply(lambda x: x + 5, axis = 1)
 
# Output
new_df

 
 Output : 

 

dataframe-apply function-2

 

Method 2: Applying user defined function to each row/column 
Example 1: For Column  

Python3




# function to returns x*x
def squareData(x):
    return x * x
 
# import pandas and numpy packages
import pandas as pd
import numpy as np
 
# list of tuples
matrix = [(1,2,3,4),
          (5,6,7,8,),
          (9,10,11,12),
          (13,14,15,16)
         ]
 
# Creating a Dataframe object
df = pd.DataFrame(matrix, columns = list('abcd'))
 
# Applying a user defined function to
# each column that will square the given
# value
new_df = df.apply(squareData)
 
# Output
new_df

 
 Output : 

 

dataframe-apply function-3

 

Example 2: For Row  

Python3




# function to returns x*X
def squareData(x):
    return x * x
 
# import pandas and numpy library
import pandas as pd
import numpy as np
 
# List of tuples
matrix = [(1,2,3,4),
          (5,6,7,8,),
          (9,10,11,12),
          (13,14,15,16)
         ]
 
# Creating a Dataframe object
df = pd.DataFrame(matrix, columns = list('abcd'))
 
# Applying a user defined function
# to each row that will square the given value
new_df = df.apply(squareData, axis = 1)
 
# Output
new_df

 
 Output : 

 

dataframe-apply function-4

 

In the above examples, we saw how a user defined function is applied to each row and column. We can also apply user defined functions which take two arguments. 

 Example 1: For Column 

Python3




# function to returns x+y
def addData(x, y):
    return x + y
 
# import pandas and numpy library
import pandas as pd
import numpy as np
 
# list of tuples
matrix = [(1,2,3,4),
          (5,6,7,8,),
          (9,10,11,12),
          (13,14,15,16)
         ]
 
# Creating a Dataframe object
df = pd.DataFrame(matrix, columns = list('abcd'))
 
# Applying a user defined function to each
# column which will add value in each
# column by given number
new_df = df.apply(addData, args = [1])
 
# Output
print(new_df)

Output: 

dataframe-apply function

Example 2: For Row 

Python3




# function to returns x+y
def addData(x, y):
    return x + y
 
# import pandas and numpy library
import pandas as pd
import numpy as np
 
# List of tuples
matrix = [(1,2,3,4),
          (5,6,7,8,),
          (9,10,11,12),
          (13,14,15,16)
         ]
 
# Creating a Dataframe object
df = pd.DataFrame(matrix, columns = list('abcd'))
 
# Applying a user defined function to each
# row which will add value in each row by
# given number
new_df = df.apply(addData, axis = 1,
                    args = [3])
 
# Output
new_df

 
Output : 

 

dataframe-apply function

 

Method 3: Applying numpy function to each row/column 
Example 1: For Column 

Python3




# import pandas and numpy library
import pandas as pd
import numpy as np
 
# list of tuples
matrix = [(1,2,3,4),
          (5,6,7,8,),
          (9,10,11,12),
          (13,14,15,16)
         ]
 
# Creating a dataframe object
df = pd.DataFrame(matrix, columns = list('abcd'))
 
# Applying a numpy function to each
# column by squaring each value
new_df = df.apply(np.square)
 
# Output
new_df

 
 Output : 

 

dataframe-apply function-5

 

Example 2: For Row 

Python3




# import pandas and numpy library
import pandas as pd
import numpy as np
 
# List of tuples
matrix = [(1,2,3,4),
          (5,6,7,8,),
          (9,10,11,12),
          (13,14,15,16)
         ]
 
# Creating a dataframe object
df = pd.DataFrame(matrix, columns = list('abcd'))
 
# Apply a numpy function to each row
# to find square root of each value
new_df = df.apply(np.sqrt, axis = 1)
 
# Output
new_df

 
 Output : 

 

dataframe-apply function

 

Method 4: Applying a Reducing function to each row/column 
A Reducing function will take row or column as series and returns either a series of same size as that of input row/column or it will return a single variable depending upon the function we use.

 

Example 1: For Column 

Python3




# import pandas and numpy library
import pandas as pd
import numpy as np
 
# List of tuples
matrix = [(1,2,3,4),
          (5,6,7,8,),
          (9,10,11,12),
          (13,14,15,16)
         ]
 
# Creating a Dataframe object
df = pd.DataFrame(matrix, columns = list('abcd'))
 
# Applying a numpy function to get the sum
# of all values in each column
new_df = df.apply(np.sum)
 
# Output
new_df

 
 Output : 

 

dataframe-apply function-7

 

Example 2: For Row 
 

Python3




# import pandas and numpy library
import pandas as pd
import numpy as np
 
# List of tuples
matrix = [(1,2,3,4),
          (5,6,7,8,),
          (9,10,11,12),
          (13,14,15,16)
         ]
 
# Creating a Dataframe object
df = pd.DataFrame(matrix, columns = list('abcd'))
 
# Applying a numpy function to get t
# he sum of all values in each row
new_df = df.apply(np.sum, axis = 1)
 
# Output
new_df

 
 Output : 

 

dataframe-apply function-8

 


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