In R, how can I find the average number of occurrences of items in a data set column?

Question

I currently have a dataset called "DT" that looks like:

Name 
A11
B16
B16
B16
B16
B98
B98
M88
K99
K99
K99

This is a subset of the real dataset, which is around 5 million rows. What I seek to do is to find the average number of occurrences for each name. That is, if I could create a new dataset that looks like:

Count
1
4
2
1
3

then it would be very trivial to just take the column sum and divide by the length. I am currently working with the data.table package and am trying to play around with the .N feature, but haven't been able to come close. the best I've done is:

DT[,`:=` .N, by = Name]

I feel like I am missing just a little something, can anyone lead me to the right direction? Thanks!

Answer 1

You can do

DT[,.N,by=Name]

#> DT
#    Name N
# 1:  A11 1
# 2:  B16 4
# 3:  B98 2
# 4:  M88 1
# 5:  K99 3