Hi,
Here is an implemenation:
> date
key_column begin_date end_date
1 123456 2013-01-01 2014-01-01
2 123456 2013-07-01 2014-07-01
3 789102 2012-03-01 2014-03-01
4 789102 2015-02-01 2016-02-01
5 789102 2015-02-06 2016-02-06
> y <- t(sapply(unique(date$key_column),function(x)
> c(x,min(as.character(date[date$key_column==x,"begin_date"])),max(as.character(date[date$key_column==x,"end_date"])))))
> y
[,1] [,2] [,3]
[1,] "123456" "2013-01-01" "2014-07-01 "
[2,] "789102" "2012-03-01" "2016-02-06"
> colnames(y)
NULL
> colnames(y) <- c("key_column","begin_date","end_date")
> y
key_column begin_date end_date
[1,] "123456" "2013-01-01" "2014-07-01 "
[2,] "789102" "2012-03-01" "2016-02-06"
--
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