Lesson 3

Hello and welcome! In today's lesson, you'll learn how to display and interpret summary statistics for categorical data within the *Diamonds* dataset. By the end of this lesson, you'll know how to group data by categories and generate meaningful statistical summaries using Python's data science libraries such as `pandas`

and `numpy`

.

Grouping data by categories is a fundamental part of **Exploratory Data Analysis** (EDA). It allows us to segment our dataset into different categories and analyze each group separately. For example, if you have sales data from multiple cities, you might want to group the data by city to understand sales performance in each location.

In Python, we achieve this using the `groupby()`

function from the `pandas`

library. This function groups data by one or more columns, which enables us to apply aggregation functions like mean, median, or standard deviation to each group.

Before proceeding with analysis, it is crucial to ensure that the data is in the right format. In this lesson, we'll focus on the `price`

column, which should be numeric to compute summary statistics.

We'll use the `pd.to_numeric()`

function to ensure that the `price`

column contains numeric values. This function converts values to numeric types, and we'll use the `errors='coerce'`

parameter to convert any invalid parsing into NaNs.

Python`1import seaborn as sns 2import pandas as pd 3 4# Load the diamonds dataset 5diamonds = sns.load_dataset('diamonds') 6 7# Ensure the 'price' column is numeric (for teaching purposes) 8diamonds['price'] = pd.to_numeric(diamonds['price'], errors='coerce') 9 10# Verify the change 11print(diamonds['price'].dtypes)`

The output of the above code will be:

Plain text`1int64`

This confirms that the `price`

column has been successfully converted to a numeric data type, specifically an integer (`int64`

). This conversion is critical for performing numerical operations and aggregations on the data.

Now that our data is ready, we will group it by the `cut`

column. This column represents the quality of the diamond cut and has categorical values like 'Fair', 'Good', 'Very Good', 'Premium', and 'Ideal'.

We will use the `groupby()`

function to group the dataset by `cut`

. The `observed=False`

parameter ensures that all possible category levels, even those not present in the data, are included in the analysis.

Python`1import seaborn as sns 2import pandas as pd 3 4# Load the diamonds dataset 5diamonds = sns.load_dataset('diamonds') 6 7# Group by 'cut' 8grouped_by_cut = diamonds.groupby('cut', observed=False)`

By grouping the data, we can perform aggregated calculations on each group, allowing us to explore how various statistics differ across different cuts of diamonds.

After grouping the data, we will calculate summary statistics such as mean, median, and standard deviation for the `price`

column. These statistics will help us understand the distribution of diamond prices across different cuts.

We'll use the `agg()`

function to perform multiple aggregations at once.

Python`1import seaborn as sns 2import pandas as pd 3 4# Load the diamonds dataset 5diamonds = sns.load_dataset('diamonds') 6grouped_by_cut = diamonds.groupby('cut', observed=False) 7 8# Calculate summary statistics 9summary_stats = grouped_by_cut['price'].agg(['mean', 'median', 'std']) 10print(summary_stats)`

The output of the above code will be:

Plain text`1 mean median std 2cut 3Ideal 3457.541970 1810.0 3808.401172 4Premium 4584.257704 3185.0 4349.204961 5Very Good 3981.759891 2648.0 3935.862161 6Good 3928.864452 3050.5 3681.589584 7Fair 4358.757764 3282.0 3560.386612`

This table shows the average (mean), median, and standard deviation of the price for diamonds across different cuts. It highlights the variability in diamond prices and helps in understanding how the quality of the cut influences price. For example, diamonds with an "Ideal" cut have a lower median price compared to other cuts, suggesting that the highest-quality cuts are not always the most expensive.

In this lesson, we covered the essential steps to display summary analysis by category. We started by introducing the concept of grouping data, then loaded and inspected the Diamonds dataset. Ensuring data quality was the next step, followed by grouping the data by the `cut`

category and calculating summary statistics.

These skills are crucial for any data scientist conducting EDA as they enable you to generate and interpret essential descriptive statistics. Up next, you'll have practice exercises to reinforce your understanding and improve your hands-on skills.

Mastering these tasks will enhance your ability to explore and understand datasets effectively. Keep practicing, and you'll gain more confidence with each step!