head() and tail() for previewing in Pandas - Step-by-Step Execution

Concept Flow - head() and tail() for previewing

Load DataFrame

↓

Call head(n)

→Return first n rows

↓

Call tail(n)

→Return last n rows

↓

Preview data subset

You start with a DataFrame, then use head() to see the first few rows or tail() to see the last few rows for a quick preview.

Execution Sample

Pandas

import pandas as pd

df = pd.DataFrame({'A': range(1, 6), 'B': list('abcde')})
print(df.head(3))
print(df.tail(2))

This code creates a small DataFrame and shows the first 3 rows and last 2 rows using head() and tail().

Execution Table

Step	Action	Input	Output
1	Create DataFrame	{'A': [1,2,3,4,5], 'B': ['a','b','c','d','e']}	DataFrame with 5 rows and 2 columns
2	Call df.head(3)	n=3	Rows 0 to 2: A B 0 1 a 1 2 b 2 3 c
3	Call df.tail(2)	n=2	Rows 3 to 4: A B 3 4 d 4 5 e

💡 All requested rows returned; preview complete

Variable Tracker

Variable	Start	After head(3)	After tail(2)
df	None	Full DataFrame with 5 rows	Full DataFrame with 5 rows
head_result	None	DataFrame with rows 0,1,2	DataFrame with rows 0,1,2
tail_result	None	None	DataFrame with rows 3,4

Key Moments - 2 Insights

Why does head(3) show rows 0,1,2 and not 1,2,3?

Because pandas DataFrame rows are zero-indexed, so the first row is index 0. head(3) returns the first 3 rows starting at index 0, which are rows 0,1,2 as shown in execution_table step 2.

What happens if n in head(n) or tail(n) is larger than the DataFrame size?

The function returns all rows without error. For example, if n=10 but DataFrame has 5 rows, head(10) or tail(10) returns all 5 rows. This is safe and shown by the exit_note.

Visual Quiz - 3 Questions

Look at the execution table, what rows does df.head(3) return?

A Rows 0, 1, 2

B Rows 1, 2, 3

C Rows 2, 3, 4

D Rows 3, 4, 5

💡 Hint

Check execution_table row 2 under Output to see which rows are returned by head(3).

At which step do we get the last 2 rows of the DataFrame?

A Step 1

B Step 2

C Step 3

D No step returns last rows

💡 Hint

Look at execution_table row 3 where tail(2) is called and returns rows 3 and 4.

If we call df.tail(10) on this DataFrame, what will happen?

A Returns last 10 rows, error if less than 10

B Returns all 5 rows without error

C Returns empty DataFrame

D Returns first 10 rows

💡 Hint

Refer to key_moments about behavior when n is larger than DataFrame size.

Concept Snapshot

head(n) returns the first n rows of a DataFrame.
tail(n) returns the last n rows.
If n is omitted, default is 5.
Useful for quick data preview without loading all rows.
Rows are zero-indexed, so first row is index 0.

Full Transcript

This lesson shows how to preview data in pandas using head() and tail(). We start with a DataFrame of 5 rows and 2 columns. Calling head(3) returns the first 3 rows, which are rows with index 0, 1, and 2. Calling tail(2) returns the last 2 rows, with index 3 and 4. These functions help us quickly see parts of the data without printing everything. If the number requested is larger than the DataFrame size, all rows are returned safely. Remember, pandas uses zero-based indexing for rows. This visual trace helps understand how head() and tail() work step-by-step.