How to modify a 2d Scatterplot to display color based on a third array in a CSV file?

To modify a 2D scatterplot to display color based on a third array in a CSV file, we use the c parameter in matplotlib's scatter() function. This allows us to map colors to data values, creating a visually informative plot.

Steps to Create a Color-Coded Scatterplot

• Read the CSV file with three columns of data
• Use the first two columns for X and Y coordinates
• Map the third column to colors using the c parameter
• Add a colorbar to show the color-to-value mapping

Example with Sample Data

Let's create a complete example that generates sample data and displays a color-coded scatterplot ?

import pandas as pd
import matplotlib.pyplot as plt
import numpy as np

# Create sample CSV data
data = {
    'x_values': [1, 2, 3, 4, 5, 6, 7, 8, 9],
    'y_values': [45, 98, 75, 54, 23, 35, 46, 57, 68],
    'colors': [71, 65, 29, 63, 12, 27, 39, 44, 51]
}
df = pd.DataFrame(data)

# Set figure size
plt.rcParams["figure.figsize"] = [8.00, 6.00]
plt.rcParams["figure.autolayout"] = True

# Create the scatter plot with colors based on third column
fig = plt.figure()
ax = fig.add_subplot(111)

# Use 'c' parameter to map colors from the third column
scatter = ax.scatter(df.x_values, df.y_values, c=df.colors, marker="*", s=100, cmap='viridis')

# Add colorbar to show color mapping
plt.colorbar(scatter, label='Color Values')

# Add labels and title
ax.set_xlabel('X Values')
ax.set_ylabel('Y Values') 
ax.set_title('2D Scatterplot with Color Mapping')

plt.show()

Key Parameters

Working with CSV Files

For actual CSV data, replace the sample data creation with file reading ?

# Read from actual CSV file
df = pd.read_csv("input.csv")

# Create scatter plot with color mapping
scatter = plt.scatter(df['data1'], df['data2'], c=df['data3'], 
                     marker="*", s=100, cmap='plasma')

# Add colorbar
plt.colorbar(scatter, label='Data3 Values')

Popular Colormaps

• viridis - Purple to yellow gradient
• plasma - Purple to pink gradient
• coolwarm - Blue to red gradient
• jet - Blue to red rainbow

Conclusion

Use the c parameter in scatter() to map colors from a third data column. Add a colorbar with plt.colorbar() to make the color mapping clear to viewers.