Summarize rows with identical identifiers with earliest start and latest end and highest value in data.table R

Question

Following data.table

dt <- data.table(
  ID= c(1,2,2,2,2),
  Value1 = c('a','b','a','a','a'),
  Start = c('2001-01-01','2000-01-01','2000-02-02','2000-03-03','2000-03-03'),
  End = c('2002-01-01','2001-01-01','2001-02-02','2001-03-03','2001-03-03'),
  Value_max = c(2,50,20,40,80)
)
   ID Value1      Start        End Value_max
1:  1      a 2001-01-01 2002-01-01         2
2:  2      b 2000-01-01 2001-01-01        50
3:  2      a 2000-02-02 2001-02-02        20
4:  2      a 2000-03-03 2001-03-03        40
5:  2      a 2000-03-03 2001-03-03        80

I want to combine rows with identical ID and Value1 extracting earliest Start , latest End and highest Value_max . I have used dt[,SD.[which.max(Value_max)],by=.c(ID,Value1)] but don't know how to combine it with the earliest start and end date.

Answer 1

min and max seem to be enough:

dt[,.(earliest = min(Start),latest = max(End), value_max = max(Value_max)),by=.(ID,Value1)]
   ID Value1   earliest     latest value_max
1:  1      a 2001-01-01 2002-01-01         2
2:  2      b 2000-01-01 2001-01-01        50
3:  2      a 2000-02-02 2001-03-03        80