Hi: A ddply solution:
library(plyr) somedata = data.frame(week=rep(1:26,rep(5,26)),day=rep(1:5,26)) # sample two rows out of five per week daysamp <- function(x) x[sample(1:5, 2), ] # Ram it through ddply: ddply(somedata, .(week), daysamp) First part of output: week day 1 1 4 2 1 3 3 2 2 4 2 1 5 3 4 6 3 1 7 4 1 8 4 5 (52 rows in all, as expected) HTH, Dennis On Fri, Mar 12, 2010 at 12:06 PM, Hosack, Michael <mhos...@state.pa.us>wrote: > Fellow R users, > > I am stumped on what would seem to be something fairly simple. > I have a dataframe that has a variable named 'WEEK' that takes > the numbers 1:26 (26 week time-period) with each number repeated > five times consecutively (once for each weekday, Monday through > Friday). Ex. 111112222233333.....2626262626. I would like to > randomly extract two weekdays per five day week for each of > 26 weeks and store this data as a separate dataframe. I have > been unable to get the sample function to work properly. > I have also tried using the runif function to assign random > numbers to each row of my dataframe, sort the dataframe first > by week number then by random number value, and finally select > the first two elements from each week subset (26 weeks total, > giving 52 randomly selected values). I can't figure out how > to select the first two elements. My goal is to randomly > select two weekdays per week (without replacement) for each of > 26 consecutive weeks. Any advice would be greatly appreciated. > > Thank you, > > Mike > > ______________________________________________ > R-help@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. > [[alternative HTML version deleted]] ______________________________________________ R-help@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.
