plyr: colvar value corresponding to max Date
I can do this in multiple steps with summarise, joins, etc., but can't help thinking it can be accomplished in one plyr call. Here's a small example:
require(plyr) require(lubridate) data <- data.frame(
+ date = rep(as.Date(ymd(20140101 + (0:3) * 100)), 2),
+ state = rep(c("A", "B"), each = 4),
+ value = rnorm(8))
What I want is clearly
data[c(4, 8), "value"]
[1] -1.007111 -1.527541 Here are my multiple steps:
statemaxval <- ddply(data, "state", summarise, max_date = max(date)) rslt <- join(data, statemaxval, by = "state") rslt <- subset(rslt, date == max_date) rslt <- rslt[!duplicated(rslt), ] rslt$value
[1] -1.007111 -1.527541 Is there a one-step way to accomplish this? Something like ddply(data, "state", summarise, "GiveMeTheValueCorrespondingToMaxDateByState!!") Or is that only possible if there is only one unique value for a given combination of state and max(date)? Thanks, Dan