Resources

• MIT 18.05 Spring 2014 R Tutorial: 1A, 1B

Things to know

Operators

Assignment:
x <- 9

Vectors

Think: list

Create a vector:
x <- c(2, 3, 5, 7)
[1] 2 3 5 7

Shortcut to create a sequential vector:
x <- 1:10
[1] 1 2 3 4 5 6 7 8 9 10

Applying arithmetic and functions to a vector applies to each element.

Number of elements:
length(x)
[1] 10

Matrices

Think: table

Create a matrix:
y = matrix(1:10, nrow=2, ncol=5)
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    3    5    7    9
[2,]    2    4    6    8   10

Access an entry in a matrix:
y[1, 2]
[1] 3

Sum over rows:
rowSums(y)
[1] 25 30

Sum over columns:
colSums(y)
[1] 3 7 11 15 19

Size of matrix:
dim(y)
[1] 2 5

Random

Randomly sample elements:
x <- 1:10
sample(x, 3)
[1] 2 10 5

Randomly sample elements, replace (i.e., can sample again) after sampling:
sample(x, 3, replace=TRUE)