How to lowercase strings in a column in Pandas dataframe

In Pandas, you can easily lowercase all values in a column using either the .str.lower() method or .apply() method with a lambda function.

Creating a Sample DataFrame:

import pandas as pd

# creating a sample dataframe
df = pd.DataFrame({'A': ['John', 'bODAY', 'MinA', 'Peter', 'nicky'],
                  'B': ['masters', 'graduate', 'graduate',
                                   'Masters', 'Graduate'],
                  'C': [27, 23, 21, 23, 24]})
 
df

OutputLet's see how can we lowercase column names in Pandas dataframe:

Method 1: Using .str.lower()

The simplest and most common way is to use .str.lower() on the column.

df['A'] = df['A'].str.lower()
df

Output

Explanation: str.lower(): converts all the elements of the column it's appied on to lowercase, which in this case is column 'A'.

Note: .str.lower() works only on string-type columns.

Method 2: Using .apply() with lambda

You can also use ".apply()" to apply the lower() function to each element:

df['A'].apply(lambda x: x.lower())
df

Output

Explanation:

• .apply(): runs a function on each element of the column.
• lambda x: x.lower(): applies the built-in lower() method to each string.

Note: This method works the same as .str.lower() but is more flexible since you can apply any custom function inside lambda.

Related Articles:

• Pandas Tutorial
• Apply uppercase to a column in Pandas dataframe