Count number of objects in list

length(x)

Get or set the length of vectors (including lists) and factors, and of any other R object for which a method has been defined.

lengths(x)

Get the length of each element of a list or atomic vector (is.atomic) as an integer or numeric vector.

Advice for R newcomers like me : beware, the following is a list of a single object :

> mylist <- list (1:10)
> length (mylist)
[1] 1

In such a case you are not looking for the length of the list, but of its first element :

> length (mylist[[1]])
[1] 10

This is a "true" list :

> mylist <- list(1:10, rnorm(25), letters[1:3])
> length (mylist)
[1] 3

Also, it seems that R considers a data.frame as a list :

> df <- data.frame (matrix(0, ncol = 30, nrow = 2))
> typeof (df)
[1] "list"

In such a case you may be interested in ncol() and nrow() rather than length() :

> ncol (df)
[1] 30
> nrow (df)
[1] 2

Though length() will also work (but it's a trick when your data.frame has only one column) :

> length (df)
[1] 30
> length (df[[1]])
[1] 2

I spent ages trying to figure this out but it is simple! You can use length(·). length(mylist) will tell you the number of objects mylist contains.

... and just realised someone had already answered this- sorry!