I know the following looks horrible in base, but here's what I came up with. It's better to use the 'sqldf' package (see below).
library(data.table)
data1 <- data.table(date = c('2010-01-21', '2010-01-25', '2010-02-02', '2010-02-09'),
name = c('id1','id2','id3','id4'))
data2 <- data.table(beginning=c('2010-01-15', '2010-01-23', '2010-01-30', '2010-02-05'),
ending = c('2010-01-22','2010-01-29','2010-02-04','2010-02-13'),
class = c(1,2,3,4))
result <- cbind(data1,"beginning"=sapply(1:nrow(data2),function(x) data2$beginning[data2$beginning[x]<data1$date & data2$ending[x]>data1$date]),
"ending"=sapply(1:nrow(data2),function(x) data2$ending[data2$beginning[x]<data1$date & data2$ending[x]>data1$date]),
"class"=sapply(1:nrow(data2),function(x) data2$class[data2$beginning[x]<data1$date & data2$ending[x]>data1$date]))
Using the package sqldf:
library(sqldf)
result = sqldf("select * from data1
left join data2
on data1.date between data2.beginning and data2.ending")
Using data.table this is simply
data1[data2, on = .(date >= beginning, date <= ending)]
