[R] Extracting last time value

[Gabor Grothendieck]

There were errors in the code I posted. Here it is again.
See my prior post in this thread for comments.

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]

and here is what it looks like when you run it:

> 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]
(06/20/11 11:39:00) (06/21/11 11:41:00) (06/22/11 14:06:00)
                  9                   8                   6



On Jan 10, 2008 7:46 PM, Gabor Grothendieck <ggrothendieck at gmail.com> wrote:
> 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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