Factor in analysis and plotting in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a factor in R?

A factor in R is a data type used to represent categorical variables. It stores categories as levels and is useful for statistical modeling and plotting.

beginner

How do you create a factor from a character vector in R?

Use the function factor(). For example: factor(c('red', 'blue', 'red')) creates a factor with levels 'blue' and 'red'.

intermediate

Why are factors important in plotting with ggplot2?

Factors control the order and grouping of categories in plots. They help ggplot2 know how to display categorical data on axes or in colors.

intermediate

How can you change the order of levels in a factor?

Use factor(x, levels = c(...)) to specify the order of levels. This changes how categories appear in analysis and plots.

beginner

What happens if you plot a numeric variable as a factor?

The numeric values are treated as categories, not numbers. The plot will show discrete groups instead of a continuous scale.

Which R function converts a character vector to a factor?

A as.character()

B factor()

C as.numeric()

D levels()

The function factor() converts character vectors to factors.

What does the levels argument in factor() do?

A Changes factor to character

B Converts factor to numeric

C Removes unused categories

D Sets the order of categories

The levels argument sets the order of categories in the factor.

In ggplot2, how does a factor affect the x-axis?

A Shows continuous numeric scale

B Removes the axis

C Shows categories as discrete groups

D Changes color of points

Factors make ggplot2 display categories as discrete groups on the axis.

If you plot a numeric variable as a factor, what will you see?

A Discrete groups for each number

B Continuous line plot

C Error message

D No plot

Plotting numeric data as a factor treats numbers as categories, showing discrete groups.

How do you check the levels of a factor variable in R?

A levels()

B class()

C str()

D summary()

The levels() function shows the categories of a factor.

Explain what a factor is in R and why it is useful for analysis and plotting.

Think about how categories are stored and used in graphs.

Describe how you would change the order of categories in a factor and why this might matter in a plot.

Consider how the order affects what you see on the graph.