### Vector creation in R

Saving and storing numbers in R is one of the most basic skills but one of the most useful as well. You can assign the number `2`

to the variable `a`

by entering

a <- 2

at the R command line. The “<-” tells R to take the number to the right of the symbol and store it in a variable whose name is given on the left. You can also use the “=” symbol, as in

a = 2

When you make an assignment R does not print out
any information. If you want to see what value a variable has just
type the name of the variable on a line and press the enter key. (In what follows, will display the results as you will see in R, with the R command prompt `>`

followed by what you type. Lines that begin with a number if brackets such as `[1]`

are the R output.)

> a [1] 3

This allows you to do all sorts of basic operations and save the numbers:

> b <- sqrt(a*a+3) > b [1] 3.464102

If you want to get a list of the variables that you have defined in a particular session you can list them all using the ls command:

> ls() [1] "a" "b"

You are not limited to just saving a single number. You can create a
list (also called a “vector”) using the `c`

command (where `c`

stands for combine):

> a <- c(1,2,3,4,5) > a [1] 1 2 3 4 5 > a+1 [1] 2 3 4 5 6 > mean(a) [1] 3 > var(a) [1] 2.5You can get access to particular entries in the vector in the following manner:

> a <- c(1,2,3,4,5) > a[1] [1] 1 > a[2] [1] 2 > a[0] numeric(0) > a[5] [1] 5 > a[6] [1] NA

Note that the zero entry is used to indicate how the data is stored. The first entry in the vector is the first number, and if you try to get a number past the last number you get “NA.”

Examples of the sort of operations you can do on vectors is given in a next chapter.

To initialize a list of numbers the *numeric* command can be used. For
example, to create a list of 10 numbers, initialized to zero, use the
following command:

> a <- numeric(10) > a [1] 0 0 0 0 0 0 0 0 0 0

If you wish to determine the data type used for a variable the *type*
command:

> typeof(a) [1] "double"