Conditional group by join in R -

i new r , rather flumoxed following problem. have 2 vectors of dates (the vectors not aligned, nor of same length).

i want find each date in first vector next date in second vector.

veca <- as.date(c('1951-07-01', '1953-01-01', '1957-04-01', '1958-12-01',        '1963-06-01', '1965-05-01')) vecb <- as.date(c('1952-01-12', '1952-02-01', '1954-03-01', '1958-08-01',             '1959-03-01', '1964-03-01', '1966-05-01')) 

in sql write this, cannot find tips in how in r.

 select veca.date, min(vecb.date)        veca inner join vecb        on veca.date < vecb.date        group veca.date 

the output should this:

start      end 1951-07-01 1952-01-12 1953-01-01 1954-03-01 1957-04-01 1958-08-01 1958-12-01 1959-03-01 1963-06-01 1964-03-01 1965-05-01 1966-05-01 

here's possible solution using data.table rolling joins

library(data.table) dt1 <- as.data.table(veca) ## convert `data.table` object dt2 <- as.data.table(vecb) ## convert `data.table` object setkey(dt2) # key in order perform binary join res <- dt2[dt1, vecb, roll = -inf, = .eachi] # run inner join while selecting closest date  setnames(res, c("start", "end")) res #         start        end # 1: 1951-07-01 1952-01-12 # 2: 1953-01-01 1954-03-01 # 3: 1957-04-01 1958-08-01 # 4: 1958-12-01 1959-03-01 # 5: 1963-06-01 1964-03-01 # 6: 1965-05-01 1966-05-01 

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alternatively, can do:

data.table(veca=vecb, vecb, key="veca")[dt1, roll=-inf]