r - data.table backward rolling join between integer and numeric columns -


came across unexpected behavior today involving data.table's rolling join. want rolling join between integer type column , numeric type column. forward roll works expected backwards roll doesn't.

dt1<-data.table(x=as.integer(c(1,2))) dt2<-data.table(x=c(1.5))  setkey(dt1, "x") setkey(dt2, "x")  dt1[dt2, roll=true] #expected behavior    x 1: 1  dt1[dt2, roll=-inf] #unexpected behavior    x 1: 1

is bug or behavior documented? guessing looks data.table casting numeric column integer internally instead of casting integer column numeric.

this expected behavior, albeit buried warning. happens dt2$x coerced integer, neither of rolls doing , it's straight merge value of 1.

to see warning use verbose=true:

dt1[dt2, verbose = true] #coercing 'double' column i.'x' 'integer' match type of x.'x'. please avoid coercion efficiency. #starting bmerge ...done in 0 secs #   x #1: 1

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