Data Wrangling in Python: Tips and Tricks
Tags: python, datascience, dataengineering
Published: 2023-03-01 12:53:17


Data wrangling, also known as data cleaning or data preprocessing, is an essential step in data analysis. It involves transforming raw data into a format suitable for analysis, which can involve tasks such as handling missing values, dealing with outliers, formatting data correctly, and more.
In this article, we'll cover some common data wrangling tasks in Python and provide tips and tricks to help you perform these tasks efficiently and effectively.

  **Handling Missing Values**

Handling missing values is a crucial step in data wrangling. Missing data can significantly impact the accuracy and reliability of your analysis, so it's essential to handle them appropriately. Here's how you can handle missing values in Python:

_Check for missing values:_

```

import pandas as pd
# Load data
data = pd.read_csv('data.csv')
# Check for missing values
print(data.isnull().sum())
```

_Remove missing values:_

```

# Remove rows with missing values
data.dropna(inplace=True)
# Remove columns with missing values
data.dropna(axis=1, inplace=True)
```

 _Impute missing values:_

```

# Impute missing values with mean
data.fillna(data.mean(), inplace=True)
# Impute missing values with median
data.fillna(data.median(), inplace=True)
```

 **Dealing with Outliers**

Outliers are values that are significantly different from the other values in the dataset. They can have a significant impact on the results of your analysis, but if they are not handled correctly, they can distort the data. Here's how you can deal with outliers in Python:

_Check for outliers:_

```

import seaborn as sns
# Load data
data = sns.load_dataset('tips')
# Check for outliers
sns.boxplot(x=data['total_bill'])
```

 _Remove outliers:_

```
# Remove outliers with z-score
from scipy import stats
z_scores = stats.zscore(data['total_bill'])
abs_z_scores = abs(z_scores)
filtered_entries = (abs_z_scores < 3)
data = data[filtered_entries]
```

 _Transform outliers:_

```

# Transform outliers with log transformation
import numpy as np
data['total_bill'] = np.log(data['total_bill'])
```

 **Formatting Data Correctly**

Data that is not formatted correctly can cause issues when analyzing the data. It's essential to ensure that all data is in the correct format and that the columns and rows are labeled correctly. Here's how you can format data correctly in Python:

_Convert data types:_

```
# Convert data type to integer
data['age'] = data['age'].astype(int)
# Convert data type to datetime
data['date'] = pd.to_datetime(data['date'], format='%Y-%m-%d')
```

_Rename columns:_

```
# Rename columns
data.rename(columns={'old_name': 'new_name'}, inplace=True)

```
 _Reorder columns:_

```
# Reorder columns
data = data[['column1', 'column2', 'column3']]
```

**Validating Data**

Validating data is an essential step to ensure that it is accurate and reliable. Failing to validate data can lead to incorrect results and conclusions. Here's how you can validate data in Python:

_Check for duplicates:_

```
# Check for duplicates
print(data.duplicated().sum())
# Remove duplicates
data.drop_duplicates(inplace=True)
```

 _Check for consistency:_

```

# Check for consistency
unique_values = data['column'].unique()
if len(unique_values) > 1:
    print(f"Warning: Column 'column' has inconsistent values: {unique_values}")
else:
    print("Column 'column' has consistent values.")
```
In conclusion, data wrangling is a crucial step in data analysis that involves cleaning, formatting, and validating data to ensure that it is accurate and reliable. By using Python, we can perform common data-wrangling tasks efficiently and effectively, including handling missing values, dealing with outliers, formatting data correctly, and validating data.

By using the tips and tricks provided in this article, you can become a more proficient data wrangler, and ensure that your data analysis is accurate and reliable. Remember to always check your data for consistency, and to handle missing data and outliers appropriately. With these tools in your toolkit, you'll be well-equipped to tackle any data-wrangling challenges that come your way.
Thank you for reading.