Hi all, I'm very novice in data.table management, and I have the following
doubt about this data: > DT <- data.table(obs=1:7, id=c(1,1,1,4,4,4,4),
time=c(3,4,7,5,8,10,15))> DT obs id time1: 1 1 32: 2 1 43: 3 1
74: 4 4 55: 5 4 86: 6 4 107: 7 4 15 In general, I know
that I can select respectively the first and the last observation within "id"
group with: First observation: DT[!duplicated(id)] Last observation:
DT[!duplicated(id, fromLast=T)] But, how can I add a new column, called
"value", which contains all zeros except:1) The first observation within each
"id" group, which is equal to 22) The last observation within each "id" group,
which is equal to 1 ? obs id time value1: 1 1 3 22: 2 1 4
03: 3 1 7 14: 4 4 5 25: 5 4 8 06: 6 4 10
07: 7 4 15 1 I've tried with conditionslas, ifelse, etc, but I get an
error message. Please, can you help me? Thanks in advance!!
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