[R] get latest dates for different people in a dataset

[William Dunlap]

Here is one way.  Sort the data.frame, first by Name then break ties with
CheckInDate.
Then choose the rows that are the last in a run of identical Name values.

> txt <- "Name    CheckInDate      Temp
+ John      1/3/2014              97
+ Mary     1/3/2014              98.1
+ Sam       1/4/2014              97.5
+ John      1/4/2014              99"
> d <- read.table(header=TRUE,
colClasses=c("character","character","numeric"), text=txt)
> d$CheckInDate <- as.Date(d$CheckInDate, as.Date, format="%d/%m/%Y")
> isEndOfRun <- function(x) c(x[-1] != x[-length(x)], TRUE)
> dSorted <- d[order(d$Name, d$CheckInDate), ]
> dLatestVisit <- dSorted[isEndOfRun(dSorted$Name), ]
> dLatestVisit
  Name CheckInDate Temp
4 John  2014-04-01 99.0
2 Mary  2014-03-01 98.1
3  Sam  2014-04-01 97.5


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Fri, Jan 23, 2015 at 3:43 PM, Tan, Richard <RTan at panagora.com> wrote:

> Hi,
>
> Can someone help for a R question?
>
> I have a data set like:
>
> Name    CheckInDate      Temp
> John      1/3/2014              97
> Mary     1/3/2014              98.1
> Sam       1/4/2014              97.5
> John      1/4/2014              99
>
> I'd like to return a dataset that for each Name, get the row that is the
> latest CheckInDate for that person.  For the example above it would be
>
> Name    CheckInDate      Temp
> John      1/4/2014              99
> Mary     1/3/2014              98.1
> Sam       1/4/2014              97.5
>
>
> Thank you for your help!
>
> Richard
>
>
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>
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