• One of the most useful functions is c()
  • Stands for combine or concatenate
  • We can join two (or more) objects into one object

z <- c(x, y)
z

## [1] 2 3

• The ability for an R object to hold more than one value:
  • Vectors are the fundamental unit in R
  • Are a 1-dimensional set of values
  • We can apply functions to an entire vector

sqrt(z)
2^z
length(z)

Q: What issues might crop up when applying a function to a vector?

Hint: What types of values exist?

Q: What issues might crop up when applying a function to a vector?

• Can we perform mathematical calculations on words?
• Can we use numbers with decimal points to indicate positions in a ranked list?

All values in a vector must be the same type of value

1. logical (TRUE or FALSE)
2. integer
3. numeric (or double): Numbers with decimal points
4. character

• Two other types we'll ignore:
  • raw (bytes) and complex (\(i =\sqrt{-1}\))

z > 0

## [1] TRUE TRUE

z == 2

## [1]  TRUE FALSE

• Lloyd will spend more time on logical vectors later

We can coerce some types of values into another type

typeof(z)
as.logical(z)
as.integer(z)
as.character(z)

Note that as you start typing the name of the function, RStudio will start to guess what you want

This is known as auto-completion

homeR <- c(742, "Evergreen", "Terrace")
length(homeR)

## [1] 3

typeof(homeR)

## [1] "character"

Q: Is my street number saved as an: integer, double or character?

Can we convert this to any of the other vector types?

as.numeric(homeR)
as.logical(homeR)

Try it and see…

Can we convert this to any of the other vector types?

as.numeric(homeR)
as.logical(homeR)

• Welcome to your first official error message!
  • Does Warning message: NAs introduced by coercion make any sense?
  • R was able to coerce "742" to a numeric value
  • R was unable to coerce the other words (for obvious reasons)

There is a trap for young players…

• When loading external data, R would traditionally convert text to categorical variables (factors)
• Each value is changed to an integer specifying which category the value is from
  • The category name is given as an additional attribute (i.e. a level)
    
  • More memory efficient for true categorical variables
  • Very common in statistical analysis

Automatic conversion is not as common now, but important to know about!

groups <- c("A", "A", "B")
groups <- as.factor(groups)
groups

## [1] A A B
## Levels: A B

Now prepare to be amazed…

typeof(groups)
levels(groups)
as.integer(groups)
as.logical(groups)

Before the next section:

1. Go to the Environment Tab
2. Click the "Broom" icon ()
3. Answer Yes to the question "Are you sure…"

We've just deleted all our R objects and have a clean Environment