Loops to assign a unique ID to a column

-----Oorspronkelijk bericht-----
Van: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
Namens Chandra Salgado Kent
Verzonden: dinsdag 2 augustus 2011 9:12
Aan: r-help at r-project.org
Onderwerp: [R] Loops to assign a unique ID to a column

Dear R help,



I am fairly new in data management and programming in R, and am trying to
write what is probably a simple loop, but am not having any luck. I have a
dataframe with something like the following (but much bigger):



Dates<-c("12/10/2010","12/10/2010","12/10/2010","13/10/2010",
"13/10/2010", "13/10/2010")

Groups<-c("A","B","B","A","B","C")

data<-data.frame(Dates, Groups)



I would like to create a new column in the dataframe, and give each distinct
date by group a unique identifying number starting with 1, so that the resulting
column would look something like:



ID<-c(1,2,2,3,4,5)



The loop that I have started to write is something like this (but doesn't work!):



data$ID<-as.number(c())

for(i in unique(data$Dates)){

  for(j in unique(data$Groups)){ data$ID[i,j]<-i

  i<-i+1

  }

}



Am I on the right track?



Any help on this is much appreciated!



Chandra


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