Pandas – Select Rows where each column has equal values

This tutorial will discuss about different ways to select DataFrame rows where each column has equal values.

Table Of Contents

Preparing DataSet

Let’s create a DataFrame with some hardcoded data.

import pandas as pd

data = {'Col_A': [21, 12, 33, 14, 35, 36, 17],
        'Col_B': [21, 22, 33, 24, 25, 36, 27],
        'Col_C': [21, 32, 33, 35, 35, 36, 35]}

index = ['X1', 'X2', 'X3', 'X4', 'X5', 'X6', 'X7']

# Create a DataFrame from a dictionary
df = pd.DataFrame.from_dict(data)

# Set the index list as Index of DataFrame
df.set_index(pd.Index(index), inplace=True)

print (df)

Output

    Col_A  Col_B  Col_C
X1     21     21     21
X2     12     22     32
X3     33     33     33
X4     14     24     35
X5     35     25     35
X6     36     36     36
X7     17     27     35

We will now select rows from this DataFrame where each column has equal values.

Select DataFrame Rows with equal values in all columns

To select only those rows from the DataFrame, which contains the equal values in all the columns, we are going to apply a Lambda function on each row of the DataFrame. Inside the Lambda function, we will create a set containing the all the row values, and the if the size of set is 1, then it means all the values in that particular row are equal.

To apply a Lambda function on each row we are going to use the apply() method of DataFrame. We will pass this lambda function as first argument and axis=1 as the second argument in the apply() method. It will apply the Lambda function of each row of the DataFrame, and it will returns a boolean series, where each True value in the boolean series represented that the particular row has equal values in all the columns.

Then we will pass this boolean series into the loc[] attribute of the DataFrame, and it will return a DataFrame containing only those rows which has same values in all the columns. Let’s see the complete example.

# Select rows with equal values in all columns
subDf = df.loc[df.apply(lambda row: len(set(row)) == 1, axis=1) ]

print (subDf)

Output

    Col_A  Col_B  Col_C
X1     21     21     21
X3     33     33     33
X6     36     36     36

Summary

We learned how to select DataFrame Rows where all values in the row are equal. Thanks.