Encoding Categorical Features

Lesson Introduction

Welcome! Today, we're learning about Encoding Categorical Features . Have you ever thought about how computers understand things like colors, car brands, or animal types? These are categorical features . Computers are good at understanding numbers but not words, so we convert these words into numbers. This process is called encoding . Our goal is to understand categorical features, why they need encoding, and how to use OneHotEncoder and LabelEncoder from SciKit Learn to do this. By the end, you'll be able to transform categorical data into numerical data for machine learning.

Introduction to Categorical Features

First, let's understand categorical features . Think about categories you see daily, like different types of fruits (apple, banana, cherry) or car colors (red, blue, green). These are examples of categorical features because they represent groups. In machine learning, these features must be converted to numbers to be understood. Why encode these features? Machine learning algorithms only work with numerical data. It's like translating a book to another language; we convert categorical features to numbers so our models can "read" the data. If a dataset includes car colors like Red, Blue, and Green, our model won't understand these words. We transform them into numbers for the model to use.

Introducing OneHotEncoder

One-hot encoding is a method to convert categorical data into a numerical format by creating binary columns for each category. Each column represents one category, and contains a 1 if the category is present and a 0 if it is not. Here, let's look at an example for a better understanding. We will encode data with OneHotEncoder step-by-step. Python import pandas as pd from sklearn.preprocessing import OneHotEncoder data = {'Feature': ['A', 'B', 'C', 'A']} df = pd.DataFrame(data) import pandas as pd from sklearn.preprocessing import OneHotEncoder data = {'Feature': ['A', 'B', 'C', 'A']} df = pd.DataFrame(data) We import Pandas and OneHotEncoder from SciKit Learn . Pandas handles data, and OneHotEncoder converts categorical features to numbers. Then, we create a small dataset with the letters A, B, C, and A, which will be our categories. Though this one particular dataset is just an example, you can face something similar in the real data. Imagine processing data about IT-companies offices, where each office is assigned with a class: A, B or C!

Join the 1M+ learners on CodeSignal

Be a part of our community of 1M+ users who develop and demonstrate their skills on CodeSignal

Encoding Specific Columns

Sometimes, you might have a dataset with multiple columns, but you only want to encode specific categorical columns. You can achieve this by directly accessing and transforming the specified columns.

To use OneHotEncoder on a specific column, you can fit and transform that column separately and then concatenate it back to the original DataFrame.

Python

import pandas as pd
from sklearn.preprocessing import OneHotEncoder

# Original dataset
data = {
    'Category': ['A', 'B', 'C', 'A'],
    'Value': [10, 20, 30, 40]
}
df = pd.DataFrame(data)

# Initializing the OneHotEncoder
encoder = OneHotEncoder(sparse_output=False)

# Fit and transform the 'Category' column
encoded_category = encoder.fit_transform(df[['Category']])

# Create a DataFrame for the encoded columns
encoded_columns = encoder.get_feature_names_out(['Category'])
encoded_df = pd.DataFrame(encoded_category, columns=encoded_columns)

# Concatenate the encoded columns back to the original DataFrame
df_encoded = pd.concat([encoded_df, df.drop('Category', axis=1)], axis=1)
print(df_encoded)

import pandas as pd
from sklearn.preprocessing import OneHotEncoder

# Original dataset
data = {
    'Category': ['A', 'B', 'C', 'A'],
    'Value': [10, 20, 30, 40]
}
df = pd.DataFrame(data)

# Initializing the OneHotEncoder
encoder = OneHotEncoder(sparse_output=False)

# Fit and transform the 'Category' column
encoded_category = encoder.fit_transform(df[['Category']])

# Create a DataFrame for the encoded columns
encoded_columns = encoder.get_feature_names_out(['Category'])
encoded_df = pd.DataFrame(encoded_category, columns=encoded_columns)

# Concatenate the encoded columns back to the original DataFrame
df_encoded = pd.concat([encoded_df, df.drop('Category', axis=1)], axis=1)
print(df_encoded)

This will produce a DataFrame that looks like:

   Category_A  Category_B  Category_C  Value
0         1.0         0.0         0.0     10
1         0.0         1.0         0.0     20
2         0.0         0.0         1.0     30
3         1.0         0.0         0.0     40

   Category_A  Category_B  Category_C  Value
0         1.0         0.0         0.0     10
1         0.0         1.0         0.0     20
2         0.0         0.0         1.0     30
3         1.0         0.0         0.0     40

Notice that only the 'Category' column is encoded, while the 'Value' column remains unchanged.

Lesson Introduction

Introduction to Categorical Features

Introducing OneHotEncoder

Join the 1M+ learners on CodeSignal

Working with OneHotEncoder

Using the `drop` Parameter in OneHotEncoder

Encoding Specific Columns

Introducing LabelEncoder

Practical Importance of OneHotEncoder and LabelEncoder

Lesson Summary