create list based on data frame in R

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I have a data frame A in the following format

user         item
10000000     1      # each user is a 8 digits integer, item is up to 5 digits integer
10000000     2
10000000     3
10000001     1
10000001     4
..............

What I want is a list B, with users' names as the name of list elements, list element is a vector of items corresponding to this user.

e.g

B = list(c(1,2,3),c(1,4),...)

I also need to paste names to B.

Thanks

asked 32 secs ago

Jin

187