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Drop rows from the dataframe based on certain condition applied on a column
  • Last Updated : 05 Feb, 2019

Pandas provides a rich collection of functions to perform data analysis in Python. While performing data analysis, quite often we require to filter the data to remove unnecessary rows or columns.

We have already discussed earlier how to drop rows or columns based on their labels. However, in this post we are going to discuss several approaches on how to drop rows from the dataframe based on certain condition applied on a column. Retain all those rows for which the applied condition on the given column evaluates to True.

To download the CSV used in code, click here.

You are given the “nba.csv” dataset. Drop all the players from the dataset whose age is below 25 years.

Solution #1 : We will use vectorization to filter out such rows from the dataset which satisfy the applied condition.






# importing pandas as pd
import pandas as pd
  
# Read the csv file and construct the 
# dataframe
df = pd.read_csv('nba.csv')
  
# Visualize the dataframe
print(df.head(15)
  
# Print the shape of the dataframe
print(df.shape)

Output :

In this dataframe, currently, we are having 458 rows and 9 columns. Let’s use vectorization operation to filter out all those rows which satisfy the given condition.




# Filter all rows for which the player's
# age is greater than or equal to 25
df_filtered = df[df['Age'] >= 25]
  
# Print the new dataframe
print(df_filtered.head(15)
  
# Print the shape of the dataframe
print(df_filtered.shape)

Output :


As we can see in the output, the returned dataframe only contains those players whose age is greater than or equal to 25 years.
 
Solution #2 : We can use the DataFrame.drop() function to drop such rows which does not satisfy the given condition.




# importing pandas as pd
import pandas as pd
  
# Read the csv file and construct the 
# dataframe
df = pd.read_csv('nba.csv')
  
# First filter out those rows which
# does not contain any data
df = df.dropna(how = 'all')
  
# Filter all rows for which the player's
# age is greater than or equal to 25
df.drop(df[df['Age'] < 25].index, inplace = True)
  
# Print the modified dataframe
print(df.head(15))
  
# Print the shape of the dataframe
print(df.shape)

Output :


As we can see in the output, we have successfully dropped all those rows which do not satisfy the given condition applied to the ‘Age’ column.

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