Brilliant - thanks for all the really useful suggestions, problem = solved.
Many thanks, Ben Gillespie, Research Postgraduate o-------------------------------------------------------------------o School of Geography, University of Leeds, Leeds, LS2 9JT o-------------------------------------------------------------------o Tel: +44(0)113 34 33345 Mob: +44(0)770 868 7641 o-------------------------------o http://www.geog.leeds.ac.uk/ o-------------------------------------o @RiversBenG o--------------o ________________________________________ From: arun [[email protected]] Sent: 17 November 2013 16:48 To: R help Cc: Berend Hasselman; Benjamin Gillespie Subject: Re: [R] Extract values from vector and repeat by group Hi, ?merge() sometimes change the order. For example: df1 <- df[-12,] df2 <- df1 merge(df1, df1[df1$time == 4, c("group", "var")], by.x = "group", by.y = "group", suffixes = c("", "GroupSK0")) In that case, df1$ord1 <- with(df1,order(group,time)) res <- merge(df1, df1[df1$time == 4, c("group", "var")], by.x = "group", by.y = "group", suffixes = c("", "GroupSK0")) res[order(res$ord1),-4] #or just library(plyr) join(df2,df2[df2$time==4,c("group","var")],by="group",type="inner") #or you may use: indx <- with(df1,ave(time==4,group,FUN=any)) ddply(df1[indx,],.(group),mutate,new=var[time==4]) A.K. On Sunday, November 17, 2013 10:22 AM, Berend Hasselman <[email protected]> wrote: On 17-11-2013, at 15:47, Benjamin Gillespie <[email protected]> wrote: > Hi all, > > I hope you can help. > > I have a data frame 'df': > > group=c(rep(1,8),rep(2,10),rep(3,11)) > var=rnorm(29) > time=c(seq(1,8),seq(1,10),seq(1,11)) > df=data.frame(group,var,time) > > I would like to extract the value from 'var' for each 'group' at 'time'=4 and > repeat these extracted values in a new vector ('new') n times where n is the > number of rows for each group. I did this by hand as below, but there must be > a quicker way: > > subset=subset(df,df$time==4) > subset > group var time > 4 1 0.2531270 4 > 12 2 -0.3600128 4 > 22 3 0.4194730 4 > > df$new=c(rep(0.2531270,8),rep(-0.3600128,10),rep(0.4194730,11)) > > Any questions please ask, A very similar question was recently asked on Stackoverflow: http://stackoverflow.com/questions/19971763/r-programming-normalizing-a-column-of-data-by-another-entry-in-2-other-columns >From the answer given there you could try this set.seed(11) # to make it reproducible group=c(rep(1,8),rep(2,10),rep(3,11)) var=rnorm(29) time=c(seq(1,8),seq(1,10),seq(1,11)) df=data.frame(group,var,time) #df #df[df$time==4, c("group", "var")] # merge into original data.frame df <- merge(df, df[df$time == 4, c("group", "var")], by.x = "group", by.y = "group", suffixes = c("", "GroupSK0")) df Berend ______________________________________________ [email protected] 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. ______________________________________________ [email protected] 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.
