Variable information

Question 1

is.na(x), is.null(x), is.array(x), is.data.frame(x), is.numeric(x), is.complex(x), is.character(x), …

Answer 1

test for type

Question 2

length(x)

Answer 2

number of elements in x

Question 3

dim(x)

Answer 3

Retrieve or set the dimension of an object; dim(x) <- c(3,2)

Question 4

dimnames(x)

Answer 4

Retrieve or set the dimension names of an object

Question 5

nrow(x)

Answer 5

number of rows; NROW(x) is the same but treats a vector as a one-
row matrix

Question 6

ncol(x)

Answer 6

id. for columns

Question 7

class(x)

Answer 7

get or set the class of x; class(x)

Question 8

unclass(x)

Answer 8

remove the class attribute of x

Question 9

attr(x,which)

Answer 9

get or set the attribute which of x

Question 10

attributes(obj)

Answer 10

get or set the list of attributes of obj