🎨 Drawing Pictures with Numbers: Line Plots & Markers

The Story of the Magic Pencil

Imagine you have a magic pencil that can draw pictures using numbers. This pencil is called Matplotlib! Instead of drawing freehand, you tell it exactly where to put dots and lines using coordinates—like playing connect-the-dots, but you’re the one deciding where the dots go!

🖊️ Basic Line Plotting: Your First Drawing

What is a Line Plot?

Think of it like this: You’re tracking how many cookies you eat each day of the week.

A line plot connects these points with a line, showing how things change over time!

Your First Line Plot

import matplotlib.pyplot as plt

days = [1, 2, 3, 4, 5]
cookies = [2, 4, 3, 5, 7]

plt.plot(days, cookies)
plt.show()

What happens:

• days = positions on the horizontal line (x-axis)
• cookies = positions going up (y-axis)
• plt.plot() = draws the line connecting all points
• plt.show() = displays your drawing!

graph TD
    A[Your Data] --> B[plt.plot x, y]
    B --> C[Line Connects Points]
    C --> D[plt.show]
    D --> E[See Your Graph!]

📊 Plotting Multiple Lines: Many Stories, One Picture

Why Multiple Lines?

What if you want to compare YOUR cookie eating with your friend’s? Put both on the same picture!

Example: You vs Your Friend

import matplotlib.pyplot as plt

days = [1, 2, 3, 4, 5]
my_cookies = [2, 4, 3, 5, 7]
friend_cookies = [3, 2, 4, 6, 5]

plt.plot(days, my_cookies)
plt.plot(days, friend_cookies)
plt.show()

Magic! Each plt.plot() adds a new line. Matplotlib automatically picks different colors!

Adding Labels So We Know Who’s Who

plt.plot(days, my_cookies, label='Me')
plt.plot(days, friend_cookies, label='Friend')
plt.legend()
plt.show()

The label gives each line a name. plt.legend() shows a little box explaining which line is which!

✨ Line Styling: Making Lines Beautiful

The 3 Magic Properties

Every line has three things you can change:

Line Style Cheat Sheet

'-'   = ────────── (solid)
'--'  = - - - - -  (dashed)
':'   = ........... (dotted)
'-.'  = -·-·-·-·-  (dash-dot)

Example: A Styled Line

plt.plot(days, cookies,
         color='red',
         linestyle='--',
         linewidth=2)
plt.show()

This creates a red, dashed, thick line!

Color Options

You can use:

• Names: 'red', 'blue', 'green', 'orange'
• Short codes: 'r', 'b', 'g', 'k' (black)
• Hex codes: '#FF5733'

⭐ Marker Customization: Highlighting Your Points

What Are Markers?

Markers are the dots at each data point. Without markers, you only see the line. With markers, you see exactly where each value is!

Basic Markers

plt.plot(days, cookies, marker='o')
plt.show()

Now each point has a circle on it!

Marker Style Menu

Customizing Markers Further

plt.plot(days, cookies,
         marker='o',
         markersize=10,
         markerfacecolor='yellow',
         markeredgecolor='red',
         markeredgewidth=2)
plt.show()

What each does:

• marker='o' → Circle shape
• markersize=10 → How big
• markerfacecolor='yellow' → Fill color
• markeredgecolor='red' → Border color
• markeredgewidth=2 → Border thickness

graph TD
    A[Marker] --> B[Shape: o, s, ^, *]
    A --> C[Size: markersize]
    A --> D[Fill: markerfacecolor]
    A --> E[Border: markeredgecolor]

🎯 Format Strings: The Shortcut Masters

The One-Line Wonder

Instead of writing color=, linestyle=, marker= separately, you can use a format string—a tiny code that does it all!

The Formula

plt.plot(x, y, 'color + marker + linestyle')

Examples

Color Codes

Practical Example

# The long way
plt.plot(x, y, color='red',
         marker='o', linestyle='--')

# The shortcut way (same result!)
plt.plot(x, y, 'ro--')

Both create a red line with circles and dashes!

Combining Everything

import matplotlib.pyplot as plt

x = [1, 2, 3, 4, 5]
y1 = [1, 4, 9, 16, 25]
y2 = [1, 2, 3, 4, 5]

plt.plot(x, y1, 'ro-', label='Squares')
plt.plot(x, y2, 'bs--', label='Linear')
plt.legend()
plt.show()

• 'ro-' = Red circles with solid line
• 'bs--' = Blue squares with dashed line

🎪 Putting It All Together

The Complete Recipe

import matplotlib.pyplot as plt

# Your data
days = [1, 2, 3, 4, 5]
temp_morning = [15, 16, 14, 17, 18]
temp_evening = [20, 22, 19, 23, 25]

# Plot with full styling
plt.plot(days, temp_morning,
         'b^-',           # Blue triangles, solid
         label='Morning',
         linewidth=2,
         markersize=8)

plt.plot(days, temp_evening,
         'ro--',          # Red circles, dashed
         label='Evening',
         linewidth=2,
         markersize=8)

# Make it pretty
plt.xlabel('Day')
plt.ylabel('Temperature')
plt.title('Daily Temperatures')
plt.legend()
plt.show()

🌟 Quick Reference

graph TD
    A[plt.plot] --> B[Basic: x, y]
    B --> C[+ Format String]
    B --> D[+ Style Parameters]
    C --> E["'ro--' = red circle dashed"]
    D --> F[color, linestyle, marker]
    D --> G[linewidth, markersize]

Remember These Magic Words

🚀 You Did It!

You now know how to:

1. Draw basic lines with plt.plot(x, y)
2. Compare data with multiple lines
3. Style lines with colors and dashes
4. Add markers to highlight points
5. Use shortcuts with format strings

Your magic pencil is ready. Go draw some amazing data pictures! 🎨