```
require(data.table)
## simple example:
x = data.table(start=c(5,31,22,16), end=c(8,50,25,18), val2 = 7:10)
y = data.table(start=c(10, 20, 30), end=c(15, 35, 45), val1 = 1:3)
setkey(y, start, end)
foverlaps(x, y, type="any", which=TRUE) ## return overlap indices
foverlaps(x, y, type="any") ## return overlap join
foverlaps(x, y, type="any", mult="first") ## returns only first match
foverlaps(x, y, type="within") ## matches iff 'x' is within 'y'
## with extra identifiers (ex: in genomics)
x = data.table(chr=c("Chr1", "Chr1", "Chr2", "Chr2", "Chr2"),
start=c(5,10, 1, 25, 50), end=c(11,20,4,52,60))
y = data.table(chr=c("Chr1", "Chr1", "Chr2"), start=c(1, 15,1),
end=c(4, 18, 55), geneid=letters[1:3])
setkey(y, chr, start, end)
foverlaps(x, y, type="any", which=TRUE)
foverlaps(x, y, type="any")
foverlaps(x, y, type="any", nomatch=NULL)
foverlaps(x, y, type="within", which=TRUE)
foverlaps(x, y, type="within")
foverlaps(x, y, type="start")
## x and y have different column names - specify by.x
x = data.table(seq=c("Chr1", "Chr1", "Chr2", "Chr2", "Chr2"),
start=c(5,10, 1, 25, 50), end=c(11,20,4,52,60))
y = data.table(chr=c("Chr1", "Chr1", "Chr2"), start=c(1, 15,1),
end=c(4, 18, 55), geneid=letters[1:3])
setkey(y, chr, start, end)
foverlaps(x, y, by.x=c("seq", "start", "end"),
type="any", which=TRUE)
```

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