Class 12 Informatics Practices Worksheet: Accessing Rows and Columns in DataFrames

Class 12 Informatics Practices Worksheet: Accessing Rows and Columns in DataFrames

Part A: Fill in the Blanks

1. To work with DataFrames in Python, we use the __________ library.
2. The method used to access a specific column in a DataFrame is __________.
3. To access a row by its index, you use __________ indexing with the iloc method.
4. The method to access data using labels is __________.
5. To get the first few rows of a DataFrame, you use the __________ method.

Part B: True or False

1. The df.loc[] method is used to access data by integer location. (True / False)
2. You can access a column in a DataFrame using df['column_name']. (True / False)
3. The df.iloc[] method can be used to access data by label. (True / False)
4. DataFrame columns can be accessed using a dot notation like df.column_name. (True / False)
5. The df.head() method displays the last few rows of the DataFrame. (True / False)

Part C: Short Answer Questions

1. How do you access the third row of a DataFrame using integer-based indexing?
2. Write the code to select the column named Age from a DataFrame df.
3. Explain the difference between df.loc[] and df.iloc[] methods.
4. How can you select multiple columns from a DataFrame? Provide an example.
5. Write the code to access rows 5 to 10 (inclusive) of a DataFrame df using integer-based indexing.

Part D: Practical Exercises

1. Given the following DataFrame:

   python
   
   import pandas as pd
   
   data = {
       'Name': ['Alice', 'Bob', 'Charlie', 'David', 'Eva'],
       'Age': [24, 27, 22, 32, 29],
       'City': ['New York', 'Los Angeles', 'Chicago', 'Houston', 'Phoenix']
   }
   
   df = pd.DataFrame(data)
   

   Perform the following tasks:

   • Access the column City.
   • Select the row with index 2.
   • Retrieve the value of Age for the person with index 3.
   • Display the first 3 rows of the DataFrame.

2. Create a DataFrame with the following data:

   Name	Subject	Marks
   John	Math	85
   Alice	Science	92
   Bob	English	78
   Carol	History	88

   Write the code to:

   • Select the Subject column.
   • Get the rows where Marks are greater than 80.
   • Select the Name and Marks columns for the first 2 rows.

3. Given a DataFrame df with the following structure:

   
   import pandas as pd
   
   data = {
       'Product': ['A', 'B', 'C', 'D', 'E'],
       'Price': [100, 150, 200, 250, 300],
       'Stock': [50, 30, 20, 10, 5]
   }
   
   df = pd.DataFrame(data)
   

   Write code to:

   • Access the Price column.
   • Retrieve the last 2 rows of the DataFrame.
   • Access the Stock value for the product with index 1.

Part E: Code Correction

Examine the following code snippets and correct any mistakes related to accessing rows and columns in DataFrames. Rewrite the correct code.

1. import pandas as pd
   
   data = {
       'Name': ['Anna', 'Ben', 'Charlie'],
       'Age': [22, 23, 25]
   }
   
   df = pd.DataFrame(data)
   print(df[1])  # Incorrect

2. 
   import pandas as pd
   
   data = {
       'Product': ['X', 'Y', 'Z'],
       'Price': [10, 20, 30]
   }
   
   df = pd.DataFrame(data)
   print(df.loc[1, 'Price'])  # Correct
   print(df.iloc['Product'])  # Incorrect