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What is iloc in Python

Understanding iloc in Python

When you're just starting out with programming, you might feel like you've been dropped into a world with its own language. Python is one of the friendliest programming languages for beginners, but it still has its share of concepts that can be tricky at first glance. One such concept is "iloc" in Python, which is used in the context of data manipulation and analysis. Let's break it down together.

The Basics of iloc

Imagine you're in a library with thousands of books. To find a book, you'd probably use the catalog, which tells you the exact location of the book on the shelves. In Python, when you're working with tables of data, iloc serves a similar purpose. It helps you find and select data in specific locations within a table.

In Python, tables of data are often represented using a package called pandas. Pandas is like a powerful version of Excel within Python that allows you to manipulate and analyze data in a tabular form. The term iloc stands for "integer location" and it's specific to pandas. It's used to select data by its position in the data table.

DataFrames and Series: The Shelves and Books of pandas

Before we dive into iloc, let's understand the two main types of data structures in pandas: DataFrames and Series.

DataFrame: This is like a whole shelf of books. It's a 2-dimensional labeled data structure with columns of potentially different types. You can think of it as a spreadsheet or SQL table, or a dict of Series objects.

Series: This is like a single book on the shelf. It's a 1-dimensional labeled array capable of holding any data type (integers, strings, floating point numbers, Python objects, etc.).

How iloc Works

iloc is used with DataFrames and Series to select data by its position. It's like telling a friend to go to row 5, column 3 in a spreadsheet to find a specific piece of information. With iloc, you use numbers to specify the location.

Selecting with iloc in DataFrames

Let's look at a simple DataFrame and see how iloc works. First, we need to create a DataFrame:

import pandas as pd

# Creating a simple DataFrame
data = {'Name': ['Alice', 'Bob', 'Charlie', 'David'],
        'Age': [25, 30, 35, 40],
        'City': ['New York', 'Los Angeles', 'Chicago', 'Houston']}
df = pd.DataFrame(data)


This will output:

      Name  Age         City
0    Alice   25     New York
1      Bob   30  Los Angeles
2  Charlie   35      Chicago
3    David   40      Houston

Now, let's use iloc to select the second row of this DataFrame:

second_row = df.iloc[1]

This will output:

Name       Bob
Age        30
City    Los Angeles
Name: 1, dtype: object

Notice how iloc uses the number 1 to select the second row. In Python, counting starts from 0, so 1 refers to the second item.

Selecting Specific Columns with iloc

What if we want to select a specific cell in our DataFrame, like choosing a chapter from a book? We can do this by specifying both the row and the column with iloc.

# Selecting the age of Charlie
charlies_age = df.iloc[2, 1]
print("Charlie's age is:", charlies_age)

This will output:

Charlie's age is: 35

In this case, 2 is the index for the third row (where Charlie's information is), and 1 is the index for the second column (where the ages are stored).

Slicing with iloc

Slicing is like telling your friend to grab a handful of books from the shelf. In pandas, you can use iloc to select multiple rows or columns by specifying a range.

# Selecting the first two rows
first_two_rows = df.iloc[0:2]

This will output:

    Name  Age         City
0  Alice   25     New York
1    Bob   30  Los Angeles

In Python, the end number in a range is exclusive. So, 0:2 means starting from 0 up to, but not including, 2.

Intuition Behind iloc

To build an intuition for iloc, think of it as a coordinate system for your data. Just like in a game of Battleship, where you call out "B2" to target a spot, iloc uses numerical coordinates (rows and columns) to access data.

Common Mistakes and Tips

When using iloc, beginners often forget that:

  • Indexing starts at 0, not 1.
  • The end of a range is exclusive.
  • Negative numbers can be used to select from the end. For example, df.iloc[-1] selects the last row.

Practice Makes Perfect

The best way to get comfortable with iloc is to practice. Try creating your own DataFrames and using iloc to select different slices of data. Experiment with different ranges and combinations of rows and columns.


In the world of data manipulation in Python, iloc is your trusty guide to finding the exact pieces of data you need. Like a map to hidden treasure, it helps you navigate the vast sea of numbers, text, and timestamps in your DataFrames and Series. As you continue your programming journey, remember that iloc is just one of the many tools in your kit. With each use, you'll find your path to becoming a data-savvy pirate of the Python seas a little clearer. So, hoist the sails and set course for deeper understanding—one integer location at a time!