Creating a While Loop to Concat Columns from Weekly Excel Files in Pandas

Understanding the Problem

As a data analyst, working with weekly excel files can be a daunting task. The provided Stack Overflow question illustrates the challenge of extracting specific cells from each file and building a dataframe with weekly values.

The goal is to create a while loop that concatenates columns from weekly excel files, resulting in a dataframe with the desired format.

Background Information

Pandas is a powerful library for data manipulation and analysis in Python. It provides various functions for reading and writing excel files, as well as operations for merging and manipulating dataframes.

To tackle this problem, we’ll delve into the world of pandas and explore the relevant functions for concatenating columns from weekly excel files.

The Challenge: Extracting Specific Cells

The question highlights a common issue when working with large datasets: avoiding overwriting intermediate results. In this case, the while loop reassigns tr at the end of each iteration, causing unexpected behavior.

To fix this issue, we’ll introduce a new approach that avoids reassigning tr and instead creates a list of dataframes to be concatenated later.

The Solution

import pandas as pd
from datetime import date, timedelta

# Initialize variables
start_date = date(2018, 1, 1)
end_date = date(2018, 1, 14)
delta = timedelta(days=7)

# Create a list to store dataframes
dataframes = []

while start_date <= end_date:
    # Read excel file
    tr = pd.read_excel('trucks from {} to {}.xlsx'.format(start_date.strftime('%Y-%m-%d'), (start_date + delta).strftime('%Y-%m-%d')))

    # Clean up columns and rows
    tr = tr.drop('Unnamed: 0', 1)
    tr = tr.drop('Unnamed: 1', 1)
    tr = tr.drop('Unnamed: 2', 1)
    tr = tr.drop(tr.loc[:, 'Unnamed: 4':'Unnamed: 29'].head(0).columns, axis=1)
    tr = tr.loc[[34, 51, 58, 66], :]

    # Rename rows of interest
    tr = tr.rename(index={34: 'Dock 1', 51: 'Dock 2', 58: 'Dock 3', 66: 'Dock 4'})

    # Append to list of dataframes
    dataframes.append(tr)

    start_date += delta

# Concatenate dataframes
final_df = pd.concat(dataframes, axis=1)

Explanation and Example Use Cases

This solution creates a list called dataframes that stores each dataframe tr as it’s read from the excel file. After the while loop finishes, we use the pd.concat() function to concatenate all the dataframes along the columns (axis=1).

The resulting dataframe final_df contains the desired format with weekly values.

Tips and Variations

• To concatenate rows instead of columns, use axis=0.
• For more complex operations, consider using pandas’ built-in functions for merging and aggregating data.
• When working with large datasets, be mindful of memory consumption and optimize your approach accordingly.

By following this solution and adapting it to your specific needs, you can efficiently extract specific cells from weekly excel files and build a dataframe with the desired format.

Last modified on 2024-01-09