Loading CSV and Excel files in LangChain - Mini Project: Build & Apply

Loading CSV and Excel files with Langchain

📖 Scenario: You work in a small company that wants to quickly load data from CSV and Excel files to analyze customer information. You will use Langchain's file loaders to read these files easily.

🎯 Goal: Build a simple Python script using Langchain to load data from a CSV file and an Excel file, preparing the data for further processing.

📋 What You'll Learn

Create a CSV file loader using Langchain

Create an Excel file loader using Langchain

Load data from both files

Print the loaded data content

💡 Why This Matters

🌍 Real World

Loading data from CSV and Excel files is common in business to analyze customer or sales data quickly.

💼 Career

Knowing how to use Langchain loaders helps automate data ingestion for AI applications and data pipelines.

1

Setup CSV file loader

Import CSVLoader from langchain.document_loaders and create a variable called csv_loader that loads the file named customers.csv.

LangChain

# Your code here

Hint

Use CSVLoader and pass the file path as file_path="customers.csv".

2

Setup Excel file loader

Import UnstructuredExcelLoader from langchain.document_loaders and create a variable called excel_loader that loads the file named sales.xlsx.

LangChain

from langchain.document_loaders import CSVLoader

csv_loader = CSVLoader(file_path="customers.csv")
# Your code here

Hint

Use UnstructuredExcelLoader and pass the file path as file_path="sales.xlsx".

3

Load data from both files

Use the load() method on csv_loader and excel_loader to load the data. Store the results in variables called csv_data and excel_data respectively.

LangChain

from langchain.document_loaders import CSVLoader, UnstructuredExcelLoader

csv_loader = CSVLoader(file_path="customers.csv")
excel_loader = UnstructuredExcelLoader(file_path="sales.xlsx")
# Your code here

Hint

Call load() on each loader and assign the results to csv_data and excel_data.

4

Print loaded data content

Print the first item of csv_data and excel_data using print() to see the loaded document content.

LangChain

from langchain.document_loaders import CSVLoader, UnstructuredExcelLoader

csv_loader = CSVLoader(file_path="customers.csv")
excel_loader = UnstructuredExcelLoader(file_path="sales.xlsx")

csv_data = csv_loader.load()
excel_data = excel_loader.load()
# Your code here

Hint

Use print() to show the first document from each loaded list.

Practice

1. What is the main purpose of using CSVLoader in LangChain?

easy

A. To load CSV files and convert their data into documents LangChain can process

B. To save data into CSV files from LangChain documents

C. To visualize CSV data in charts

D. To convert Excel files into CSV format

Solution

1. Step 1: Understand CSVLoader's role

   CSVLoader is designed to read CSV files and transform their content into a format LangChain can use.

2. Step 2: Differentiate from other options

   Saving, visualizing, or converting files are not functions of CSVLoader.

3. Final Answer:

   To load CSV files and convert their data into documents LangChain can process -> Option A

4. Quick Check:

   CSVLoader loads CSV files = A [OK]

Hint: CSVLoader reads CSV files into LangChain documents [OK]

Common Mistakes:

• Thinking CSVLoader saves or visualizes data
• Confusing CSVLoader with ExcelLoader
• Assuming CSVLoader converts file formats

2. Which of the following is the correct way to load an Excel file named data.xlsx using LangChain's ExcelLoader?

easy

A. loader = ExcelLoader.open('data.xlsx')

B. loader = ExcelLoader.load('data.xlsx')

C. loader = ExcelLoader.read('data.xlsx')

D. loader = ExcelLoader('data.xlsx')

Solution

1. Step 1: Recall ExcelLoader instantiation

   ExcelLoader is instantiated by passing the file path as a string to its constructor.

2. Step 2: Identify correct syntax

   Only ExcelLoader('data.xlsx') correctly creates a loader instance; other methods like load(), read(), open() are invalid here.

3. Final Answer:

   loader = ExcelLoader('data.xlsx') -> Option D

4. Quick Check:

   Use constructor with filename = A [OK]

Hint: Use ExcelLoader('filename.xlsx') to create loader [OK]

Common Mistakes:

• Using non-existent methods like load() or read() on ExcelLoader
• Forgetting to pass filename as a string
• Trying to open file with open() method on loader

3. Given the code:

from langchain.document_loaders import CSVLoader
loader = CSVLoader('contacts.csv')
docs = loader.load()

What will docs contain after running this code?

medium

A. A dictionary mapping column names to values

B. A list of document objects representing rows from the CSV file

C. An error because CSVLoader requires sheet name

D. A single string with all CSV content

Solution

1. Step 1: Understand CSVLoader.load() output

   The load() method returns a list of document objects, each representing a row or chunk from the CSV file.

2. Step 2: Eliminate incorrect options

   It does not return a single string, dictionary, or error for missing sheet name (sheet names apply to ExcelLoader).

3. Final Answer:

   A list of document objects representing rows from the CSV file -> Option B

4. Quick Check:

   load() returns list of documents = D [OK]

Hint: load() returns list of documents, not raw strings [OK]

Common Mistakes:

• Expecting a string or dictionary instead of documents list
• Confusing CSVLoader with ExcelLoader sheet requirements
• Assuming load() returns raw file content

4. What is wrong with this code snippet for loading an Excel file?

from langchain.document_loaders import ExcelLoader
loader = ExcelLoader('data.xlsx', sheet_name='Sheet1')
docs = loader.load()

medium

A. The file path must be an absolute path, not relative

B. ExcelLoader does not accept sheet names when loading files

C. The parameter should be named sheet_names (plural), not sheet_name

D. The load() method must be called with the sheet name argument

Solution

1. Step 1: Check ExcelLoader sheet name parameter

   ExcelLoader expects the parameter sheet_names (plural) as a list of sheet names, not sheet_name.

2. Step 2: Validate other options

   ExcelLoader does accept sheet names, relative paths are allowed, and load() does not take sheet name arguments.

3. Final Answer:

   The parameter should be named sheet_names (plural), not sheet_name -> Option C

4. Quick Check:

   Use sheet_names list parameter = C [OK]

Hint: Use sheet_names=['Sheet1'] not sheet_name='Sheet1' [OK]

Common Mistakes:

• Using singular sheet_name instead of plural sheet_names
• Thinking load() needs sheet name argument
• Believing relative paths are invalid

5. You want to load only the 'Sales' sheet from an Excel file report.xlsx using LangChain. Which code snippet correctly does this?

hard

A. loader = ExcelLoader('report.xlsx', sheet_names=['Sales'])
docs = loader.load()

B. loader = ExcelLoader('report.xlsx', sheet_name='Sales')
docs = loader.load()

C. loader = ExcelLoader('report.xlsx')
docs = loader.load(sheet_name='Sales')

D. loader = ExcelLoader('report.xlsx')
docs = loader.load()
filter_docs = [d for d in docs if d.metadata['sheet'] == 'Sales']

Solution

1. Step 1: Use correct parameter to specify sheets

   ExcelLoader accepts sheet_names as a list of sheet names to load only those sheets.

2. Step 2: Confirm load() usage

   load() does not take sheet names; they must be specified when creating the loader.

3. Step 3: Evaluate options

   loader = ExcelLoader('report.xlsx', sheet_name='Sales') docs = loader.load() uses sheet_name (singular), incorrect. loader = ExcelLoader('report.xlsx') docs = loader.load(sheet_name='Sales') passes sheet name to load(), invalid. loader = ExcelLoader('report.xlsx') docs = loader.load() filter_docs = [d for d in docs if d.metadata['sheet'] == 'Sales'] loads all sheets then filters manually, inefficient. Only loader = ExcelLoader('report.xlsx', sheet_names=['Sales']) docs = loader.load() correctly uses sheet_names=['Sales'] at loader creation.

4. Final Answer:

   loader = ExcelLoader('report.xlsx', sheet_names=['Sales']) docs = loader.load() -> Option A

5. Quick Check:

   Use sheet_names list at loader creation = B [OK]

Hint: Pass sheet_names=['SheetName'] when creating ExcelLoader [OK]

Common Mistakes:

• Using singular sheet_name parameter
• Passing sheet name to load() method
• Loading all sheets then filtering manually