Python – Sort grouped Pandas dataframe by group size?

To group Pandas data frame, we use groupby(). To sort grouped data frames in ascending or descending order, use sort_values(). The size() method is used to get the data frame size.

Steps Involved

The steps included in sorting the panda's data frame by its group size are as follows.

• Importing the panda's library and Creating a Pandas dataframe.

• Grouping the columns by using the groupby() function and sorting the values by using sort_values() in descending order.

• Sorting the values in ascending order by using the sort_values() function.

Creating a pandas dataframe

First import the Pandas library, and create a Pandas data frame.

import pandas as pd

# dataframe with one of the columns as Reg_Price
dataFrame = pd.DataFrame({
   "Car": ['BMW', 'Lexus', 'Audi', 'Mercedes', 'Jaguar', 'Bentley'],
   "Reg_Price": [1000, 1400, 1000, 900, 1700, 900],
   
})

Grouping and Sorting

To group according to the Reg_Price column and sort in descending order by setting ascending=False

dataFrame.groupby('Reg_Price').size().sort_values(ascending=False)

Next, group according to the Reg_Price column and sort in ascending order by setting ascending=True

dataFrame.groupby('Reg_Price').size().sort_values(ascending=True)

Example

In the example code the DataFrame contains columns Car and Reg_Price. We group by the Reg_Price column using the groupby() function, and calculate the size of each group, then sort these group sizes in descending and ascending order using the sort_values() function.

import pandas as pd

# dataframe with one of the columns as Reg_Price
dataFrame = pd.DataFrame(
   {
      "Car": ['BMW', 'Lexus', 'Audi', 'Mercedes', 'Jaguar', 'Bentley'],

      "Reg_Price": [1000, 1400, 1000, 900, 1700, 900]
   }
)

print("DataFrame...\n",dataFrame)

# group according to Reg_Price column and sort in descending order
print("Sorted in Descending order...\n")
print(dataFrame.groupby('Reg_Price').size().sort_values(ascending=False))

# group according to Reg_Price column and sort in ascending order
print("Sorted in Ascending order...\n")
print(dataFrame.groupby('Reg_Price').size().sort_values(ascending=True))

Input DataFrame

Sorted in Descending order

Sorted in Ascending order