R Language Lists Introduction to lists
Example
Lists allow users to store multiple elements (like vectors and matrices) under a single object. You can use the list function to create a list:
l1 <- list(c(1, 2, 3), c("a", "b", "c"))
l1
## [[1]]
## [1] 1 2 3
##
## [[2]]
## [1] "a" "b" "c"
Notice the vectors that make up the above list are different classes. Lists allow users to group elements of different classes. Each element in a list can also have a name. List names are accessed by the names function, and are assigned in the same manner row and column names are assigned in a matrix.
names(l1)
## NULL
names(l1) <- c("vector1", "vector2")
l1
## $vector1
## [1] 1 2 3
##
## $vector2
## [1] "a" "b" "c"
It is often easier and safer to declare the list names when creating the list object.
l2 <- list(vec = c(1, 3, 5, 7, 9),
mat = matrix(data = c(1, 2, 3), nrow = 3))
l2
## $vec
## [1] 1 3 5 7 9
##
## $mat
## [,1]
## [1,] 1
## [2,] 2
## [3,] 3
names(l2)
## [1] "vec" "mat"
Above the list has two elements, named "vec" and "mat," a vector and matrix, resepcively.
