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The pandas.DataFrame.query() method filters the rows of the caller DataFrame using the given query expression.

pandas.DataFrame.query()grammar

DataFrame.query(expr, inplace=False, **kwargs)

parameter

Return Value

If inplaceis True, return the filtered DataFrame; otherwise is None.

Example code: DataFrame.query()Method with a single condition

import pandas as pd

df = pd.DataFrame({'X': [1, 2, 3,],
                   'Y': [4, 1, 8]})
print("Original DataFrame:")
print(df)

filtered_df=df.query('X>1')
print("Filtered DataFrame:")
print(filtered_df)

Output:

Original DataFrame:
   X  Y
0  1  4
1  2  1
2  3  8
Filtered DataFrame:
   X  Y
1  2  1
2  3  8

It returns DataFrameonly the rows that satisfy the given query expression, that is, only the rows Xwhere the value of column is greater 1than .

DataFrame.query()Example code: Method when column names have spaces

Before applying this method to DataFrame, we have to make sure that the column names we are querying do not have any spaces in them.

If we have spaces in our column names, we can use backticks (`).

import pandas as pd

df = pd.DataFrame(
    {
        "X": [
            1,
            2,
            3,
        ],
        "Y": [4, 1, 8],
        "A B": [3, 5, 7],
    }
)
print("Original DataFrame:")
print(df)
filtered_df = df.query("`A B`>5")
print("Filtered DataFrame:")
print(filtered_df)

Output:

Original DataFrame:
   X  Y  A B
0  1  4    3
1  2  1    5
2  3  8    7
Filtered DataFrame:
   X  Y  A B
2  3  8    7

Here, the column name A Bhas spaces. To make a query expression for that column, we enclose the column name in backticks, otherwise an error will occur.

Example code: DataFrame.query()Method with multiple conditions

import pandas as pd

df = pd.DataFrame({'X': [1, 2, 3,],
                   'Y': [4, 1, 8]})
print("Original DataFrame:")
print(df)

filtered_df=df.query('X>1' and 'Y==1')
print("Filtered DataFrame:")
print(filtered_df)

Output:

Original DataFrame:
   X  Y
0  1  4
1  2  1
2  3  8
Filtered DataFrame:
   X  Y
1  2  1

If we want to filter based on multiple conditions DataFrame, we use andthe operator to combine multiple query expressions into a compound query expression.

It gives the rows in which the value of DataFramecolumn is greater than and the value of column is equal to .X1Y1

We can modify the original query()by setting after calling the method .inplace=TrueDataFrame

import pandas as pd
df = pd.DataFrame({'X': [1, 2, 3,],
                   'Y': [4, 1, 8]})
filtered_df=df.query('X>1' and 'Y==1',inplace=True)
print(df)

Output:

   X  Y
1  2  1