Array
a <- array(c(1,2,3,4,5,6,7,8,9,10,11,12),dim=c(3,4))
> a
[,1] [,2] [,3] [,4]
[1,] 1 4 7 10
[2,] 2 5 8 11
[3,] 3 6 9 12
a vector with the same contents:
> v <- c(1,2,3,4,5,6,7,8,9,10,11,12) > v [1] 1 2 3 4 5 6 7 8 9 10 11 12
matrix is just a two-dimensional array:
> m <- matrix(data=c(1,2,3,4,5,6,7,8,9,10,11,12),nrow=3,ncol=4)
> m
[,1] [,2] [,3] [,4]
[1,] 1 4 7 10
[2,] 2 5 8 11
[3,] 3 6 9 12
Arrays can have more than two dimensions. For example:
> w <- array(c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18),dim=c(3,3,2))
> w
, , 1
[,1] [,2] [,3]
[1,] 1 4 7
[2,] 2 5 8
[3,] 3 6 9
, , 2
[,1] [,2] [,3]
[1,] 10 13 16
[2,] 11 14 17
[3,] 12 15 18
Lists in R are subtly different from lists in many other languages. Lists in R may contain a heterogeneous selection of objects. You can name each component in a list. Items in a list may be referred to by either location or name.
> e <- list(thing=”hat”, size=”8.25″) > e $thing [1] “hat” $size [1] “8.25″
A list can even contain other lists:
> g <- list(“this list references another list”, e) > g [[1]] [1] “this list references another list” [[2]] [[2]]$thing [1] “hat” [[2]]$size [1] “8.25″
A data frame is a list that contains multiple named vectors that are the same length. A data frame is a lot like a spreadsheet or a database table. Data frames are particularly good for representing experimental data.
> teams <- c("PHI","NYM","FLA","ATL","WSN")
> w <- c(92, 89, 94, 72, 59)
> l <- c(70, 73, 77, 90, 102)
> nleast <- data.frame(teams,w,l)
> nleast
teams w l
1 PHI 92 70
2 NYM 89 73
3 FLA 94 77
4 ATL 72 90
5 WSN 59 102
