Error in lis[[i]] : attempt to select less than one element - r

Question

This code is meant to compute the total distance of some given coordinates, but I don't know why it's not working.
The error is: Error in lis[[i]] : attempt to select less than one element.
Here is the code:
distant<-function(a,b)
{
return(sqrt((a[1]-b[1])^2+(a[2]-b[2])^2))
}
totdistance<-function(lis)
{
totdis=0
for(i in 1:length(lis)-1)
{
totdis=totdis+distant(lis[[i]],lis[[i+1]])
}
totdis=totdis+distant(lis[[1]],lis[[length(lis)]])
return(totdis)
}
liss1<-list()
liss1[[1]]<-c(12,12)
liss1[[2]]<-c(18,23)
liss1[[4]]<-c(29,25)
liss1[[5]]<-c(31,52)
liss1[[3]]<-c(24,21)
liss1[[6]]<-c(36,43)
liss1[[7]]<-c(37,14)
liss1[[8]]<-c(42,8)
liss1[[9]]<-c(51,47)
liss1[[10]]<-c(62,53)
liss1[[11]]<-c(63,19)
liss1[[12]]<-c(69,39)
liss1[[13]]<-c(81,7)
liss1[[14]]<-c(82,18)
liss1[[15]]<-c(83,40)
liss1[[16]]<-c(88,30)
Output:
> totdistance(liss1)
Error in lis[[i]] : attempt to select less than one element
> distant(liss1[[2]],liss1[[3]])
[1] 6.324555

Answer 1

Let me reproduce your error in a simple way
>list1 = list()
> list1[[0]]=list(a=c("a"))
>Error in list1[[0]] = list(a = c("a")) :
attempt to select less than one element
So, the next question is where are you accessing 0 index list ?
(Indexing of lists starts with 1 in R )
As Molx, indicated in previous posts : "The : operator is evaluated before the subtraction - " . This is causing 0 indexed list access.
For ex:
> 1:10-1
[1] 0 1 2 3 4 5 6 7 8 9
>1:(10-1)
[1] 1 2 3 4 5 6 7 8 9
So replace the following lines of your code
>for(i in 1:(length(lis)-1))
{
totdis=totdis+distant(lis[[i]],lis[[i+1]])
}