merging endpoints of a range with a sequence

Question

In one of my application there is a piece of code that retrieve information from a data.table object depending on values in another.

# say this tabl         


        

Answer 1

This is a great spot to use the roll argument of data.table:

setkey(dt1, id, date)
setkey(dt, id, start)

dt[dt1, roll = TRUE][end >= start,
   list(start = start[1], end = end[1], result = mean(var)), by = id]

# benchmark
microbenchmark(OP    = adply(dt, 1, myfunc),
               Frank = dt[dt1[as.list(dt[,seq.Date(start,end,"day"),by="id"])][,mean(var),by=id]],
               eddi  = dt[dt1, roll = TRUE][end >= start,list(start = start[1], end = end[1], result = mean(var)), by = id])
#Unit: milliseconds
#  expr       min        lq    median        uq       max neval
#    OP 24.436126 29.184786 30.853094 32.493521 50.898664   100
# Frank  9.115676 11.303691 12.081000 13.122753 28.370415   100
#  eddi  5.336315  6.323643  6.771898  7.497285  9.531376   100

The time difference will become much more dramatic as the size of the datasets grows.