How to Find Percentile Stats of a Given Column Using Pandas

As a data scientist or software engineer, you might come across a situation where you need to analyze the distribution of a dataset and find the percentile statistics of a specific column. In such cases, Pandas is the go-to library for data manipulation and analysis in Python. In this post, we will discuss how to find percentile statistics of a given column using Pandas.

Table of Contents

1. What are Percentile Statistics?
2. Step-by-Step Guide to Finding Percentile Statistics Using Pandas
3. Common Errors
4. Best Practices
5. Conclusion

What are Percentile Statistics?

Percentiles are used to divide a dataset into equal parts based on the value of a specific column. For example, the 50th percentile (also known as the median) is the value that divides the dataset into two equal parts. Similarly, the 25th percentile (also known as the first quartile) is the value that divides the dataset into four equal parts. Percentile statistics are useful in understanding the distribution of a dataset and identifying outliers.

Let’s consider the following DataFrame:

       name  age  salary
0     Alice   25   95767
1       Bob   30   50967
2   Charlie   52   52042
3     David   46   98117
4       Eva   46   96719
5     Frank   51   86764
6     Grace   50   62443
7     Henry   46   58686
8       Ivy   30   95121
9      Jack   58   59271
10    Katie   38   70260
11     Liam   47   97618
12      Mia   48   68332
13   Nathan   47   54634
14   Olivia   37   89439
15     Paul   28   88806
16    Quinn   51   69256
17   Rachel   31   64053
18      Sam   52   85306
19    Tyler   59   68671

Step-by-Step Guide to Finding Percentile Statistics Using Pandas

To find percentile statistics of a given column using Pandas, we will follow these steps:

1. Import the Pandas library and read the dataset into a Pandas DataFrame.
2. Identify the column for which you want to find percentile statistics.
3. Use the quantile() function to find the percentile statistics.

Let’s dive into each step in detail.

Step 1: Import the Pandas Library and Read the Dataset into a Pandas DataFrame

To use Pandas, we first need to import the library. We can do this using the following code:

import pandas as pd

Next, we need to read the dataset into a Pandas DataFrame. We can use the read_csv() function to read a CSV file into a DataFrame. For example, if our dataset is stored in a file called data.csv, we can read it into a DataFrame using the following code:

df = pd.read_csv('data.csv')

Step 2: Identify the Column for Which You Want to Find Percentile Statistics

Once we have the dataset loaded into a DataFrame, we need to identify the column for which we want to find percentile statistics. We can do this by referring to the column name. For example, if we want to find percentile statistics for the age column, we can use the following code:

column_name = 'age'

Step 3: Find the Percentile Statistics

Use the quantile() Function

The quantile() function is used to find the percentile statistics of a given column in a Pandas DataFrame. We can use this function to find any percentile, such as the median (50th percentile), first quartile (25th percentile), third quartile (75th percentile), etc.

The quantile() function takes a single argument, which is the percentile value as a decimal. For example, to find the median (50th percentile), we can use the following code:

median = df[column_name].quantile(0.5)
print(median)

Output:

46.5

Similarly, to find the first quartile (25th percentile) and third quartile (75th percentile), we can use the following code:

q1 = df[column_name].quantile(0.25)
q3 = df[column_name].quantile(0.75)

We can also find any other percentile by specifying the percentile value as a decimal. For example, to find the 90th percentile, we can use the following code:

p90 = df[column_name].quantile(0.9)

Method 2: Using numpy.percentile

import numpy as np

# Load the employee data CSV file into a Pandas DataFrame
df = pd.read_csv('data.csv')

# Extract the salary column for analysis
salary_data = df['salary']

# Define the desired percentiles
percentiles = [25, 50, 75]

# Calculate percentiles using numpy.percentile
percentile_values = np.percentile(salary_data, percentiles)

print(f"Salary Percentiles {percentiles}: {percentile_values}")

Output:

Salary Percentiles [25, 50, 75]: [68100.5  75557.   88517.25]

Common Errors

Error 1: Missing Data

Handle missing data appropriately using methods like dropna or imputation, especially if your dataset contains missing salary values.

Error 2: Incorrect Percentile Value

Ensure that the specified percentile values are within the valid range (0 to 100 for numpy.percentile and 0 to 1 for Pandas' quantile).

Best Practices

• Handle missing data appropriately using methods like dropna or imputation.
• Verify column names and ensure they match your DataFrame structure.
• Choose the method that best suits your needs; numpy.percentile for more flexibility or Pandas' quantile for simplicity.

Conclusion

In this post, we discussed how to find percentile statistics of a given column using Pandas. We learned that percentile statistics are useful in understanding the distribution of a dataset and identifying outliers. We also went through a step-by-step guide to finding percentile statistics using Pandas. By following these steps, you can easily find the percentile statistics of any column in a Pandas DataFrame.

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