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
Hi,
Try ?which.max() # unique values for the combination.

?ddply(data,.(state),summarize,max_date=value[which.max(date)])[,2]
#or
?ddply(data,.(state),summarize,max_date=value[date == max(date)])[,2]

A.K.
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

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and provide commented, minimal, self-contained, reproducible code.
ddply(data, "state", function(x) x[x$date == max(x$date), ])$value
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

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Thank you A.K. and Ista. The answer that eliminates duplicated rows is
A.K.'s first solution (brilliant idea using which.max!).
The version of Ista's solution without duplicates is
ddply(data, "state", function(x) x[which.max(x$date), ])$value
Thanks again!
Dan
Hi,
Try ?which.max() # unique values for the combination.

 ddply(data,.(state),summarize,max_date=value[which.max(date)])[,2]
#or
 ddply(data,.(state),summarize,max_date=value[date == max(date)])[,2]

A.K.

On Thursday, February 13, 2014 11:15 AM, Dan Murphy <chiefmurphy at gmail.com> wrote:
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

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.