Color scales and palettes in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a basic colorRampPalette function

What is the output of this R code snippet?

R Programming

pal <- colorRampPalette(c("red", "blue"))
colors <- pal(3)
print(colors)

A [1] "#FF0000" "#400080" "#0000FF"

B [1] "red" "purple" "blue"

C [1] "#FF0000" "#FF00FF" "#0000FF"

D [1] "#FF0000" "#800080" "#0000FF"

💡 Hint

colorRampPalette creates a gradient of colors between the given colors.

colorRampPalette interpolates colors between red (#FF0000) and blue (#0000FF). For 3 colors, the middle color is the average, which is purple (#800080).

🧠 Conceptual

intermediate

Understanding colorRamp vs colorRampPalette

Which statement correctly describes the difference between colorRamp and colorRampPalette in R?

A colorRampPalette interpolates colors as numeric RGB values; colorRamp returns hex color strings.

B colorRamp generates a vector of colors; colorRampPalette returns RGB values only.

C colorRamp returns a function that interpolates colors as RGB values; colorRampPalette returns a function that generates a vector of colors as hex strings.

D Both functions return the same output but differ in input format.

💡 Hint

Think about what type of output each function produces.

colorRamp returns a function that gives numeric RGB values between colors, while colorRampPalette returns a function that produces hex color strings suitable for plotting.

❓ Predict Output

advanced

Output of a custom palette with transparency

What is the output of this R code?

R Programming

pal <- colorRampPalette(c("#FF000080", "#0000FF80"), alpha = TRUE)
colors <- pal(2)
print(colors)

A [1] "#FF0000FF" "#0000FFFF"

B [1] "#FF000080" "#0000FF80"

C [1] "#FF0000" "#0000FF"

D [1] "#FF0080" "#000080"

💡 Hint

Check how colorRampPalette handles alpha transparency in hex colors.

colorRampPalette preserves the alpha transparency in hex colors when generating the palette.

❓ Predict Output

advanced

Number of colors generated by brewer.pal

What is the length of the vector returned by brewer.pal(5, "Set1") in R?

R Programming

library(RColorBrewer)
colors <- brewer.pal(5, "Set1")
length(colors)

A 5

B 8

C 3

D 7

💡 Hint

brewer.pal returns the number of colors requested up to the palette maximum.

brewer.pal(5, "Set1") returns exactly 5 colors from the Set1 palette.

🔧 Debug

expert

Identify the error in this colorRampPalette usage

What error does this R code produce?

R Programming

pal <- colorRampPalette(c(123, 456))
colors <- pal(3)
print(colors)

A Error in colorRampPalette: 'colors' must be character vector

B Error in pal(3): invalid number of colors requested

C No error; outputs three colors

D Error in print: object 'colors' not found

💡 Hint

Check the input types for colorRampPalette.

colorRampPalette expects a character vector of colors; numeric values cause an error.