How to Calculate Percentiles of a Column in Python

In the realm of statistics and data analysis, percentiles are used to understand and interpret data. A percentile of a given set of data is the value below which a certain percentage of the data falls.

This tutorial will guide you through the process of calculating percentiles of a column in Python. This is specifically beneficial in exploratory data analysis or when you want to dive a bit more into your data.

Step 1: Importing Necessary Libraries

To begin calculating percentiles, we’ll first need to import some necessary libraries. In Python, both Pandas and Numpy are powerful tools for data analysis and they offer built-in functions to calculate percentiles.

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import pandas as pd
import numpy as np

Step 2: Creating a DataFrame

Let’s create a simple DataFrame with a column named ‘Data’ that contains random integers.

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data = pd.DataFrame({
    'Data': np.random.randint(0, 100, 100)
})

Step 3: Calculate and Display Percentiles

To calculate percentiles, we can use Pandas, Numpy, or both. The numpy.percentile() function takes an array of values and a number as arguments, and returns the given percentile value.

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percentiles = np.percentile(data['Data'], [25, 50, 75])
print(percentiles)

You may replace [25, 50, 75] with any numbers corresponding to the percentile you want to calculate. For example, use [10, 20, 30] to calculate 10th, 20th, and 30th percentiles respectively.

Step 4: Interpreting the Results

The output will be an array with the percentile values in the same order as specified in the function. These are the 25th, 50th, and 75th percentile values respectively, also known as the first quartile, median, and third quartile respectively.

Step 5: Apply Multiple Percentiles

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percentiles = data['Data'].quantile([0.1, 0.5, 0.9])
print(percentiles)

This way, you can quickly find multiple percentiles using the quantile function, which returns the values at the given quantiles.

The Full Code

Okay, before moving to the conclusion, let’s see the whole Python script to calculate percentiles:

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import pandas as pd
import numpy as np
 
data = pd.DataFrame({
    'Data': np.random.randint(0, 100, 100)
})
 
percentiles = np.percentile(data['Data'], [25, 50, 75])
print(percentiles)
 
percentiles = data['Data'].quantile([0.1, 0.5, 0.9])
print(percentiles)

Conclusion

In conclusion, calculating percentiles in Python is breeze, thanks to great libraries like Pandas and Numpy. Being able to calculate and understand percentiles can greatly help in making sense of a data set and extracting insights from it.

Remember, practice makes perfect. So, keep exploring and manipulating data, apply the learned methods to different datasets and observe the results.