CODEWITHSUNDEEP
r
WestCoastProjects
WestCoastProjects

Reputation: 63259

Length of a list with multiple entries is 1?

From the following code we can see there is a 2D array of list's:

> coldists[3,4]
[[1]]
     mean        sd 
0.5752512 0.4067640 
> class(coldists[3,4][1])
[1] "list"
> class(coldists[3,4][[1]])
[1] "numeric"

My confusion is: why is the length of the list reported as [1] instead of [2] ?

length(coldists[3,4])
[1] 1

After all there appear to be 2 entries (mean and sd) in that list ..

Upvotes: 1

Views: 55

Answers (2)

Paul
Paul

Reputation: 9107

It is a list containing a vector with two elements.

x <- list(c(mean = 0.5752512, sd = 0.4067640))
x
#> [[1]]
#>      mean        sd 
#> 0.5752512 0.4067640

Because it only contains one vector, it has length one.

length(x)
#> [1] 1

However, when we get the length of the vector, it has length 2. 

length(x[[1]])
#> [1] 2

When we use single brackets, it gets a sublist rather than extracting the vector. This sublist is still a length one list containing a vector with two elements.

length(x[1])
#> [1] 1

Upvotes: 3

S&#233;bastien Rochette
S&#233;bastien Rochette

Reputation: 6671

Here, coldists[3,4] is a list with one element. Inside this unique list element there is a vector of length 2 (mean, sd). If you want to have the length of the vector inside the list, you need to specify it like : length(coldists[3,4][[1]])

Upvotes: 2

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