Lowercase in Python Tutorial

Using str.lower() in Pandas

When working with pandas DataFrames, the str.lower() method is often applied to an entire column of strings to standardize text formatting. Let’s look at an example to see how it works.

Here’s a sample dataset representing the prices of different fruits:

import pandas as pd

# Create a DataFrame
fruit_price = pd.DataFrame({
    'name': [
        'Apple', 'Banana', 'Orange', 'Watermelon',
        'Plum', 'Blueberries', 'Dragonfruit', 'Kiwi'
    ],
    'price_usd': [0.88, 0.23, 0.68, 3.98, 0.96, 5.16, 5.27, 1.12]
})

            name      price_usd
0          Apple           0.88
1         Banana           0.23
2         Orange           0.68
3     Watermelon           3.98
4           Plum           0.96
5    Blueberries           5.16
6    Dragonfruit           5.27
7           Kiwi           1.12 

We can apply the str.lower() method to convert all entries in the name column to lowercase. Here’s how it’s done:

fruit_price['name'] = fruit_price['name'].str.lower()
print(fruit_price)

Here's the output:

            name      price_usd
0          apple           0.88
1         banana           0.23
2         orange           0.68
3     watermelon           3.98
4           plum           0.96
5    blueberries           5.16
6    dragonfruit           5.27
7           kiwi           1.12

As you can see, all entries in the name column are now standardized to lowercase.

Interactive Example: Changing Case in a Movie Dataset

Let’s explore another example. Imagine we’re working with a dataset of movies. Each row in the dataset represents a movie, with columns for the title (movie_title), genre (movie_genre), and duration (movie_length). Here’s the initial dataset:

import pandas as pd

# Create a DataFrame
movies = pd.DataFrame({
    'movie_title': [
        'The Sumif All Fears', 'The Seaborn Identity', 'The Matrices',
        "There's Something About Merging", 'Mamma Median!',
        'Harry Plotter', 'Kung Fu Pandas', 'While You Were Sorting',
        '10 Things I Hate About UNIX'
    ],
    'movie_genre': [
        'Action', 'Action', 'Action', 'Comedy', 'Comedy',
        'Kids', 'Kids', 'Romance', 'Romance'
    ],
    'movie_length': [124, 119, 136, 119, 108, 159, 92, 103, 97]
})

We want to standardize the text in the movie_title column by converting all titles to lowercase. Here’s how we can achieve this using the .str.lower() method:

# Change movie_title column to lowercase
movies['movie_title'] = movies['movie_title'].str.lower()

# Look at the change
print(movies)

When you run the above code, it produces the following result:

                        movie_title movie_genre  movie_length
0              the sumif all fears      Action           124
1             the seaborn identity      Action           119
2                     the matrices      Action           136
3  there's something about merging      Comedy           119
4                    mamma median!      Comedy           108
5                    harry plotter        Kids           159
6                   kung fu pandas        Kids            92
7           while you were sorting     Romance           103
8      10 things i hate about unix     Romance            97

By applying .str.lower(), we ensure that the movie_title column is uniformly formatted, which is useful for tasks like filtering, comparisons, or performing case-insensitive operations.

Try it for yourself!

To learn more about putting pandas dataframe together in Python, please see this video from our course Python for Spreadsheet Users.

This content is taken from DataCamp's Python for Spreadsheet Users course by Chris Cardillo.