Hi, May be this helps you:
dat1<-read.table(text=" tdate event_tim transaction 1/10/2012 2 14 1/10/2012 4 28 1/10/2012 6 42 1/10/2012 8 14 2/10/2012 6 46 2/10/2012 9 64 2/10/2012 8 71 3/10/2012 3 85 3/10/2012 1 14 3/10/2012 4 28 9/10/2012 5 51 9/10/2012 9 66 9/20/2012 12 84 ",sep="",header=TRUE,stringsAsFactors=FALSE) dat2<-dat1[with(dat1,order(tdate,event_tim)),] dat2$tdate<-as.Date(dat2$tdate,format="%m/%d/%Y") dat3<-dat2 dat3$last_trans<-NA library(plyr) dat4<-merge(dat3,ddply(dat2,.(tdate),tail,1)) dat4$last_trans<-dat4$transaction res<-merge(dat4,dat2,all=TRUE) res # tdate event_tim transaction last_trans #1 2012-01-10 2 14 NA #2 2012-01-10 4 28 NA #3 2012-01-10 6 42 NA #4 2012-01-10 8 14 14 #5 2012-02-10 6 46 NA #6 2012-02-10 8 71 NA #7 2012-02-10 9 64 64 #8 2012-03-10 1 14 NA #9 2012-03-10 3 85 NA #10 2012-03-10 4 28 28 #11 2012-09-10 5 51 NA #12 2012-09-10 9 66 66 #13 2012-09-20 12 84 84 ----- Original Message ----- From: ramoss <ramine.mossad...@finra.org> To: r-help@r-project.org Cc: Sent: Friday, October 19, 2012 1:51 PM Subject: [R] Creating a new by variable in a dataframe Hello, I have a dataframe w/ 3 variables of interest: transaction,date(tdate) & time(event_tim). How could I create a 4th variable (last_trans) that would flag the last transaction of the day for each day? In SAS I use: proc sort data=all6; by tdate event_tim; run; /*Create last transaction flag per day*/ data all6; set all6; by tdate event_tim; last_trans=last.tdate; Thanks ahead for any suggestions. -- View this message in context: http://r.789695.n4.nabble.com/Creating-a-new-by-variable-in-a-dataframe-tp4646782.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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. ______________________________________________ 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.
