[R] Extracting last time value

[Gabor Grothendieck]

Here is a slight variation of ones you have already received.  This
also uses zoo.

In the DF<- line we read it in as a data frame.  In the z<- line we convert
it to zoo using chron date/times (see R News 4/1 for more).
We calculate the positions of duplicate dates and in the last line we
extract the rows corresponding to non-duplicates.

Lines <- "Date            time            value
20110620        11:18:00        7
20110620        11:39:00        9
20110621        11:41:00        8
20110621        11:40:00        6
20110622        14:05:00        8
20110622        14:06:00        6
"

library(zoo)
library(chron)
DF <- read.table(textConnection(Lines), header = TRUE, as.is = TRUE)
z <- zoo(DF$value, chron(unclass(as.Date(format(DF$Date), "%Y%m%d"))), DF$time)

isdup <- duplicated(dates(time(z)), fromLast = TRUE)
z[!isdup,]

For more on zoo see:

library(zoo)
vignette("zoo")
vignette("zoo-quickref")


On Jan 10, 2008 5:36 PM, Kondamani, Arjun (GMI - NY Corporate Bonds)
<arjun_kondamani at ml.com> wrote:
> I have a dataframe as follows:
>
> Date            time            value
> 20110620        11:18:00        7
> 20110620        11:39:00        9
> 20110621        11:41:00        8
> 20110621        11:40:00        6
> 20110622        14:05:00        8
> 20110622        14:06:00        6
>
> For every date, I want to extract the row that has the greatest time.
> Therefore, ending up like:
> 20110620        11:39:00        9
> 20110621        11:41:00        8
> 20110622        14:07:00        6
>
> I am using for loops (for every date, find largest time value) to do
> this determination, but I am sure there is a simpler way in "R". Has
> anyone run into this before?
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