loc vs iloc mental model in Pandas - Quick Revision & Key Differences

Recall & Review

beginner

What does loc do in pandas?

loc selects data by label. It uses the row and column names you see in the DataFrame.

beginner

What does iloc do in pandas?

iloc selects data by position. It uses the row and column numbers starting from 0.

beginner

If a DataFrame has row labels [10, 20, 30], what will df.loc[20] return?

It returns the row with label 20. Labels are exact matches.

beginner

If a DataFrame has 5 rows, what will df.iloc[2] return?

It returns the third row (index 2) because iloc counts rows by position starting at 0.

intermediate

How does slicing differ between loc and iloc?

loc slices include the end label (inclusive). iloc slices exclude the end position (like normal Python slices).

Which method uses row and column labels to select data?

A loc

B iloc

C ix

D at

loc uses labels. iloc uses positions.

What does df.iloc[0] return?

A First row by label

B Last row by position

C First row by position

D Last row by label

iloc selects by position, so 0 means the first row.

If row labels are [1, 3, 5], what does df.loc[3] return?

A Row at position 3

B Row at position 1

C Error

D Row with label 3

loc uses labels, so it returns the row labeled 3.

Which slicing includes the end label in pandas?

A iloc slicing

B loc slicing

C Both loc and iloc

D Neither

loc slices include the end label; iloc slices exclude the end position.

What happens if you use df.iloc[5] on a DataFrame with 5 rows?

A Raises an IndexError

B Returns the last row

C Returns the 6th row

D Returns the first row

iloc uses zero-based positions. Index 5 is out of range for 5 rows, so it raises an error.

Explain the difference between loc and iloc in pandas using a real-life example.

Think about how you find items by name versus by order.

Describe how slicing works differently with loc and iloc.

Compare to how Python normally slices lists.