## Resources

## 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)`