Ranged/Filtered Cross Join with R data.table

Question

I want to cross-join two data tables without evaluating the full cross join, using a ranging criterion in the process. In essence, I would like CJ with filtering/ranging ex

Answer 1

This seems like a problem that could benefit a lot from using interval trees algorithm. A very nice implementation is available from the bioconductor package IRanges.

# Installation
source("http://bioconductor.org/biocLite.R")
biocLite("IRanges")

# solution
require(IRanges)
ir1 <- IRanges(dt1$D, width=1L)
ir2 <- IRanges(dt2$D1, dt2$D2)

olaps <- findOverlaps(ir1, ir2, type="within")
cbind(dt1[queryHits(olaps)], dt2[subjectHits(olaps)])

   id1  D id2 D1 D2
1:   3  6  21  5  9
2:   4  8  21  5  9
3:   4  8  22  7 12
4:   5 10  22  7 12
5:   5 10  23 10 16
6:   6 12  22  7 12
7:   6 12  23 10 16
8:   7 14  23 10 16
9:   8 16  23 10 16