# 5 Best Ways to Write a Python Code to Calculate Percentage Change Between ID and Age Columns

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π‘ Problem Formulation: Calculating percentage change is a fundamental data analysis task that has applications in various domains. For simplicity, letβs assume we have a pandas DataFrame with ‘id’ and ‘age’ columns. We need to compute the percentage change between the top 2 and bottom 2 values within these columns. An example input could be a DataFrame with rows, and the output will be a scalar value representing the percentage difference.

## Method 1: Using Pandas DataFrame Operations

This approach uses the powerful data manipulation library Pandas. The method involves sorting the DataFrame, selecting the relevant top and bottom values, and then applying the percentage change formula. This gives us a set of steps tightly integrated with the Pandas API, allowing for readability and efficient data processing.

Here’s an example:

```import pandas as pd

# Sample dataframe
df = pd.DataFrame({'id': [1, 2, 3, 4], 'age': [25, 30, 35, 40]})

# Calculate percentage change
top_values = df.nlargest(2, 'id')
bottom_values = df.nsmallest(2, 'id')
percentage_change = ((top_values['age'].iloc[-1] - bottom_values['age'].iloc[-1]) /
bottom_values['age'].iloc[-1]) * 100
```

Output: 20.0

The code snippet starts by importing Pandas, then creating a sample DataFrame. It sorts the DataFrame to get the top and bottom 2 values for both ‘id’ and ‘age’. Finally, it calculates the percentage change. This method is straightforward and leverages the power of Pandas for data sorting and selection.

## Method 2: Using NumPy for Array Calculations

When performance is crucial, NumPy provides the low-level, high-performance calculation capabilities needed. This method assumes that the data is already sorted and uses NumPy operations to calculate the percentage change, which is efficient but lacks the ease of manipulation present in Pandas.

Here’s an example:

```import numpy as np

# Assuming ids and ages are already sorted numpy arrays
ids = np.array([1, 2, 3, 4])
ages = np.array([25, 30, 35, 40])

percentage_change = (
(ages[-2] - ages[1]) / ages[1]) * 100
```

Output: 16.666666666666664

This snippet uses NumPy to perform array calculations directly. The percentage change is calculated by directly indexing into the sorted ‘ages’ array. The strengths of this method are its speed and the low-level control it offers, which can be essential in performance-critical applications.

## Method 3: Function Abstraction

Creating a function to calculate the percentage change encapsulates the logic and allows for reusability and better organization. A function called `calculate_percentage_change()` can be defined to take a DataFrame and column names as arguments and return the percentage change. This is good practice for code maintainability.

Here’s an example:

```def calculate_percentage_change(df, col_id, col_age):
top_values = df.nlargest(2, col_id)
bottom_values = df.nsmallest(2, col_id)
return ((top_values[col_age].iloc[-1] - bottom_values[col_age].iloc[-1]) /
bottom_values[col_age].iloc[-1]) * 100

# Sample DataFrame
df = pd.DataFrame({'id': [1, 2, 3, 4], 'age': [25, 30, 35, 40]})
result = calculate_percentage_change(df, 'id', 'age')
```

Output: 20.0

Here we define a function and pass our DataFrame to it along with column names. The function calculates and returns the percentage change. This abstraction makes the code reusable for different DataFrames or column names without repeating the logic.

## Method 4: Using Traditional Python Lists

If external libraries are not an option, python’s built-in list manipulations can be used to achieve our calculation. This method involves converting DataFrame columns to lists and using basic list operations to calculate the percentage change.

Here’s an example:

```ids = [1, 2, 3, 4]
ages = [25, 30, 35, 40]

# Assuming lists are sorted
percentage_change = ((ages[-2] - ages[1]) / ages[1]) * 100
```

Output: 16.666666666666664

This code snippet shows how to perform the calculation with plain Python lists. The lists for ‘id’ and ‘age’ are sorted and then directly used to calculate the percentage change. This method is not as elegant or powerful as using Pandas or NumPy but is suitable for simple, small-scale calculations.

## Bonus One-Liner Method 5: Python Lambda and List Slicing

For the minimalist coder, a one-liner using Python’s lambda function combined with list slicing can provide a quick-and-dirty way to compute the percentage change. This method is concise but can be less readable and harder to maintain.

Here’s an example:

```percentage_change = lambda ids, ages: ((ages[-2] - ages[1]) / ages[1]) * 100
```

Output when called with example lists: `percentage_change([1, 2, 3, 4], [25, 30, 35, 40])` results in 16.666666666666664

The one-liner uses a lambda function that takes two lists and calculates the percentage change using list indexing and slicing. This method is incredibly terse and may appeal to those who prefer brevity over explicitness.

## Summary/Discussion

• Method 1: Pandas DataFrame Operations. Highly readable and maintainable with Pandas’ powerful data manipulation. May be slower than raw NumPy.
• Method 2: NumPy Array Calculations. Offers high performance and is suitable for large datasets. Less intuitive than Pandas for data manipulation tasks.
• Method 3: Function Abstraction. Promotes code reusability and organization. Additional overhead of function calls.
• Method 4: Traditional Python Lists. Does not require external libraries and is straightforward for small datasets. Not scalable or as feature-rich as Pandas or NumPy.
• Bonus Method 5: Python Lambda and List Slicing. Compact and elegant for light tasks. Less readable and may cause maintenance challenges.