Adding and removing categories in Pandas - Step-by-Step Execution

Concept Flow - Adding and removing categories

Start with Categorical Data

↓

Add new category

↓

Check categories updated?

No→Error or Retry

Yes↓

Remove category

↓

Check categories updated?

No→Error or Retry

Yes↓

End

Start with categorical data, add new categories, verify update, then remove categories and verify again.

Execution Sample

Pandas

import pandas as pd
cat = pd.Categorical(['a', 'b', 'a'], categories=['a', 'b'])
cat = cat.add_categories(['c'])
cat = cat.remove_categories(['b'])
print(cat.categories)

Create a categorical variable, add a new category 'c', remove category 'b', then print remaining categories.

Execution Table

Step	Action	Categories Before	Categories After	Notes
1	Create categorical with categories ['a', 'b']	[]	['a', 'b']	Initial categories set
2	Add category 'c'	['a', 'b']	['a', 'b', 'c']	New category 'c' added
3	Remove category 'b'	['a', 'b', 'c']	['a', 'c']	Category 'b' removed
4	Print categories	['a', 'c']	['a', 'c']	Final categories displayed
5	End	['a', 'c']	['a', 'c']	No more steps

💡 All categories updated correctly; execution ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
cat.categories	[]	['a', 'b']	['a', 'b', 'c']	['a', 'c']	['a', 'c']

Key Moments - 2 Insights

Why does the category list change after adding a new category?

Because add_categories adds the new category to the existing list without changing existing data, as shown in step 2 of the execution_table.

What happens to data points with a removed category?

Data points with the removed category become NaN or missing, since the category no longer exists, as implied after step 3 in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what are the categories after step 2?

A ['a', 'c']

B ['a', 'b']

C ['a', 'b', 'c']

D ['b', 'c']

💡 Hint

Check the 'Categories After' column for step 2 in the execution_table.

At which step is the category 'b' removed?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column in the execution_table to find when 'b' is removed.

If we add category 'd' after step 3, what will be the categories?

A ['a', 'c', 'd']

B ['a', 'b', 'c', 'd']

C ['a', 'b', 'd']

D ['a', 'c']

💡 Hint

After step 3, categories are ['a', 'c'], adding 'd' appends it.

Concept Snapshot

pandas Categorical categories can be changed.
Use add_categories(['new_cat']) to add.
Use remove_categories(['old_cat']) to remove.
Removing a category affects data points with it.
Always check categories after changes.

Full Transcript

We start with a pandas Categorical variable with categories 'a' and 'b'. Then we add a new category 'c' using add_categories, which updates the categories list to include 'c'. Next, we remove the category 'b' using remove_categories, which removes 'b' from the categories list. Finally, we print the categories to see the updated list, which is now ['a', 'c']. This process shows how to add and remove categories step-by-step in pandas.