Pandas query() Method

Basic Queries

1. Query rows with Courses equals “R Programming”

• Python

Python

df2=df.query("Courses == “R Programming")
print(df2)

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Output:

The output shows all the details related to the R programming course.

In the above code example, a new DataFrame is returned after filtering the rows. What if we wanted to update the existing DataFrame only, use inplace=True.

Below is the example code:

• Python

Python

df = pd.DataFrame(dsa_courses)
df2=df.query("Courses == 'R Programming'",inplace=True)

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2. Query rows with Courses Fees greater than equals 23000
 

• Python

Python

df2=df.query("Fee >= 23000")
print(df2)

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Output:

The above output shows all the course details having fees greater than or equal to 23000.

Multiple Conditions Query

Most time, we need to select the rows based on multiple conditions, and by using multiple columns, we can do it as below:

• Python

Python

print(df.query(" Fee >= 25000 and Fee <= 26000"))

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Output

The above output displays the list of all the courses whose fees are in the range of 25k to 26k

Query Rows using apply()

The DataFrame.apply() method is used to apply the expression row by row and return the rows that have values that match the expression. The below example will return every match when Courses contains a list of specified string values.

• Python

Python

print(df.apply(lambda row: row[df['Courses'].isin(['Big Data','Deep Learning'])]))

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Output:

The above code examples use a lambda expression, which is nothing but a small anonymous function that can take any number of arguments and execute an expression.

So the lambda function is applied to each row and yields the output shown above.

Query using index 

We can use the query() method in Pandas to filter out the rows based on conditions involving the index of the DataFrame. Let's see an example:

• Python

Python

print(df.query('index%2 == 0'))

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Output:

In the above code, the query 'index%2 == 0' selects all the rows from the data frame df where the index values are even. So, the output will display the list of courses that have even-number indices.

Frequently Asked Questions

Pandas query() method for index filtering be used?

The pandas query() method can be easily used with an index, like 'index%2 == 0' . This will select all the rows where the index meets the given condition, such as even values.

Pandas query() method suitable for large datasets? 

Pandas query() is suitable for large datasets, but then it may be slower. It is recommended to balance its usage with other Pandas techniques for faster analysis of large datasets.

Variables be used in the Pandas query() method?

Yes, variables can be used in the query by using @. For example, query('Fee > @max_fee') filters rows with fees higher than the value stored in the max_fee variable.

Conclusion

Congratulations, you did a fantastic job!!. This article has gone through a comprehensive guide to Pandas query() and its syntax and discussed several working examples. At last, some frequently asked questions have been discussed.

Here are some more related articles:
 

• Getting started with Pandas 
• Must Know Functions in pandas 
• Advanced functions in Pandas 
   

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