Re: [R] Extracting last time value

From: Achim Zeileis <Achim.Zeileis_at_wu-wien.ac.at>
Date: Fri, 11 Jan 2008 00:13:57 +0100 (CET)


On Thu, 10 Jan 2008, Kondamani, Arjun (GMI - NY Corporate Bonds) 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

You could use the time series functionality in "zoo" for this:

  ## data and package
  x <- read.table(textConnection("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"),
    header = TRUE, as.is = TRUE)
  library("zoo")

  ## turn data frame into a time series
  z <- zoo(x$value,
    as.POSIXct(strptime(paste(x$Date, x$time), "%Y%m%d %H:%M:%S")))

  ## aggregate
  aggregate(z, as.Date, tail, 1)

  ## or if you want to retain the associated last time   ix <- zoo(1:length(z), time(z))
  last.ix <- aggregate(ix, as.Date, tail, 1)   z[as.numeric(last.ix)]

hth,
Z

> 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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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. Received on Thu 10 Jan 2008 - 23:14:46 GMT

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