Keep only groups of data with multiple observations

Question

I am attempting to keep only deids with multiple observations.

I have the below code

help <- data.frame(deid = c(1, 5, 5, 5, 5, 5, 5, 12, 12, 12,         


        

Answer 1

this should do it - you need to filter by number of observations in each group which is got using n():

help %>% group_by(deid) %>% filter(n()>1)

  deid session.number days.since.last
1     5              1               0
2     5              2               7
3     5              3              14
4     5              4              93
5     5              5               5
6     5              6             102
7    12              1               0
8    12              2              21
9    12              3             104
10   12              4               4

Answer 2

Using data.table instead:

helpcount <- help[, list(Count = .N), by = deid]
helpf <- merge(help,helpcount, by = "deid")
helpf <- helpf[Count > 1]

EDIT: A bit more concise:

help[, Count := .N, by = deid]
help[Count > 1]

EDIT2: thelatemail's even more concise solution:

help[,if(.N > 1) .SD, by=deid]