Expand dates in data.table
data.table, r
Solution
As `seq` takes only a single element in `from` and `to`, we can group by 'id' (if there are no duplicates) and then do the `seq`
setDT(old.table)[, .(date = seq(first.date, last.date, by = '1 day')), by = ID]
# ID date
#1: 1 2001-01-01
#2: 1 2001-01-02
#3: 1 2001-01-03
#4: 2 2002-02-01
#5: 2 2002-02-02
#6: 2 2002-02-03
#7: 2 2002-02-04
If the 'ID' is also duplicated, then group by the sequence of rows instead
setDT(old.table)[, .(date = seq(first.date, last.date, by = '1 day')),
by = .(ID, ID2 = seq_len(nrow(old.table)))]
Problem
I currently have a problem, where I have a data table with start and end date together with an ID. A new table should have the same ID with one column date, containing a sequence of days between first and last day, one day for each row, i.e. ``` old.table ID first.date last.date 1 2001-01-01 2001-01-03 2 2002-02-01 2002-02-04 new table ID date 1 2001-01-01 1 2001-01-02 1 2001-01-03 2 2002-02-01 2 2002-02-02 2 2002-02-03 2 2002-02-04 ``` I know, that calling ``` seq(first.date,last.date,"day") ``` creates such a sequence. However, calling ``` old.table[,date := seq(first.date,last.date,"day")]) ``` throws the exception ``` Error in seq.Date(first.date, last.date, "day") : 'from' must be of length 1 ``` meaning, that vectorizing the input is not possible (at least not like this). Is there a way, to get the desired solution?