Plot Enhancement

🎨 Base R Visualization: Plot Enhancement

Imagine you’re an artist with a blank canvas. Base R plots are your canvas, and these enhancement tools are your paintbrushes, rulers, and frames!

🌟 The Big Picture

You’ve made a basic plot in R. Great! But it looks plain. Like a cake without frosting. Let’s add the frosting—legends, lines, text, grids, and more—to make your plots beautiful and informative.

Our Analogy: Think of your plot as a coloring book page. We’re about to add:

• Labels (so people know what colors mean)
• Extra drawings (lines and points)
• Words (text annotations)
• Ruler lines (grids)
• Frame settings (margins and arrangements)
• And finally, we’ll save our masterpiece!

📚 Legend Function

What is a Legend?

A legend is like a map key. When you color different things with different colors, the legend tells people what each color means.

Simple Example

# Draw two lines
plot(1:5, type="l", col="red")
lines(1:5 * 1.5, col="blue")

# Add a legend
legend("topleft",
       legend = c("Apples", "Oranges"),
       col = c("red", "blue"),
       lty = 1)

Key Parts of legend()

Where Can You Put It?

graph TD
    A["Legend Positions"] --> B["topleft"]
    A --> C["top"]
    A --> D["topright"]
    A --> E["left"]
    A --> F["center"]
    A --> G["right"]
    A --> H["bottomleft"]
    A --> I["bottom"]
    A --> J["bottomright"]

💡 Pro tip: Use legend("topleft", ...) to keep it out of the way of your data!

➕ Adding Lines and Points

Adding More Lines with lines()

Already drew a plot? Want to add another line on top? Use lines().

# First, make a plot
plot(1:10, 1:10, type="l", col="green")

# Add another line
lines(1:10, 10:1, col="purple")

Adding Points with points()

Want to mark specific spots? Use points().

# Make a plot
plot(1:5, 1:5)

# Add special points
points(c(2, 4), c(3, 5),
       col="red", pch=19, cex=2)

Point Symbols (pch)

Line Types (lty)

✏️ Adding Text to Plots

The text() Function

Want to write words on your plot? Like adding labels to a drawing!

plot(1:5, 1:5)

# Add text at specific spot
text(3, 4, "Hello!", col="blue")

Positioning Text

The mtext() Function

For text in the margins (edges of your plot):

plot(1:5, 1:5)

# Add margin text
mtext("Top Label", side=3)
mtext("Bottom Label", side=1)

Side numbers: 1=bottom, 2=left, 3=top, 4=right

📏 Grid Lines

Adding a Grid

Grids are like the lines on graph paper. They help you read values!

plot(1:10, 1:10)

# Add grid
grid()

Customizing Your Grid

plot(1:10, 1:10)

# Fancy grid
grid(nx = 5, ny = 5,    # 5 lines each way
     col = "lightgray",
     lty = 2)           # dashed

Using abline() for Lines

Draw straight lines anywhere!

plot(1:10, 1:10)

# Horizontal line at y=5
abline(h = 5, col = "red")

# Vertical line at x=3
abline(v = 3, col = "blue")

# Diagonal line
abline(a = 0, b = 1, col = "green")

⚙️ The par() Function

Your Plot Control Panel

par() is like the settings menu for ALL your plots. Change it once, and it affects everything after!

Common Settings

# See current settings
par()

# Change settings
par(bg = "lightyellow",   # background
    col = "darkblue",     # default color
    cex = 1.2)            # text size

Important Parameters

Saving and Restoring Settings

# Save current settings
old_par <- par()

# Make changes
par(bg = "pink")
plot(1:5)

# Restore original
par(old_par)

🔲 Multiple Plot Arrangement

mfrow and mfcol

Want to show multiple plots at once? Like a comic strip!

# 2 rows, 2 columns of plots
par(mfrow = c(2, 2))

plot(1:5, main = "Plot 1")
plot(1:5, main = "Plot 2")
plot(1:5, main = "Plot 3")
plot(1:5, main = "Plot 4")

# Reset to single plot
par(mfrow = c(1, 1))

The Difference

graph LR
    subgraph mfrow
    A["1"] --> B["2"]
    C["3"] --> D["4"]
    end

Using layout()

For unequal plot sizes:

# Create layout matrix
layout(matrix(c(1, 1, 2, 3),
              nrow = 2, byrow = TRUE))

plot(1:10, main = "Big plot")
plot(1:5, main = "Small 1")
plot(1:5, main = "Small 2")

📐 Plot Margins

Understanding mar

Margins are the empty space around your plot. Like the frame around a picture!

# mar = c(bottom, left, top, right)
par(mar = c(5, 4, 4, 2))

Default Values

graph TD
    subgraph Margins
    A["Top: 4 lines"]
    B["Right: 2 lines"]
    C["Bottom: 5 lines"]
    D["Left: 4 lines"]
    end

Making Room for Labels

# More space at bottom for long labels
par(mar = c(7, 4, 4, 2))
plot(1:5, xlab = "")
mtext("Long label here", side = 1,
      line = 5)

Outer Margins with oma

For space around multiple plots:

par(mfrow = c(2, 2),
    oma = c(2, 2, 3, 2))  # outer margins

plot(1:5); plot(1:5)
plot(1:5); plot(1:5)

mtext("Main Title", outer = TRUE,
      side = 3, cex = 1.5)

💾 Saving Plots to Files

Why Save Plots?

So you can use them in reports, presentations, or share with friends!

PNG Format (Pictures)

# Start saving
png("my_plot.png",
    width = 800, height = 600)

# Make your plot
plot(1:10, main = "My Plot")

# Stop saving
dev.off()

PDF Format (Documents)

pdf("my_plot.pdf",
    width = 8, height = 6)

plot(1:10, main = "My Plot")

dev.off()

Other Formats

Key Parameters

Complete Example

# Save a fancy plot
png("final_plot.png",
    width = 800,
    height = 600,
    res = 100)

par(mar = c(5, 4, 4, 2))
plot(1:10, 1:10,
     col = "blue",
     pch = 19,
     main = "My Data")
grid()
legend("topleft",
       legend = "Points",
       pch = 19,
       col = "blue")

dev.off()  # Don't forget this!

⚠️ Important: Always call dev.off() when you’re done! Otherwise, your file won’t save properly.

🎯 Quick Reference Flow

graph TD
    A["Create Basic Plot"] --> B["Add Data"]
    B --> C{Enhance?}
    C --> D["legend - add key"]
    C --> E["lines/points - add data"]
    C --> F["text/mtext - add labels"]
    C --> G["grid/abline - add guides"]
    D --> H["par - adjust settings"]
    E --> H
    F --> H
    G --> H
    H --> I["Save to file"]

🌈 You Did It!

You now know how to:

• ✅ Add legends to explain your colors
• ✅ Draw extra lines and points
• ✅ Write text anywhere on your plot
• ✅ Add helpful grid lines
• ✅ Control all settings with par()
• ✅ Arrange multiple plots together
• ✅ Adjust margins for perfect spacing
• ✅ Save your masterpiece to a file

Remember: Every great data visualization starts simple and gets enhanced one step at a time. You’ve got all the tools now—go make something beautiful! 🎨