[R] Label rows of table by factor level for groups of factors

[O'Hanlon, Simon J]

Dear useRs,
I am sure this is a fairly simple problem, but I just cannot get my head around it.


I have a dataframe which contains several factor variables. I can use table() to tell me how many different combinations there are of these variables. What I should like to do is to add a column to my original dataframe which labels each row according to the unique combination of factors.


E.g. in the simple example below I create a dataframe 'df' with 3 columns, the values of which take 0 or 1. I can then classify each row in the table and I find that I have 4 unique combinations of factors. I would now like to add a fourth column to df which labels each row according to whether it was unique combination 1,2,3 or 4:

x1=c(rep(0:1,6))
x2=c(rep(c(1,1,0,0)6))
x3=c(rep(1,6),rep(0,6))
df=data.frame(x1,x2,x3)
tabledf=as.data.frame(with(df, table(x1,x2,x3)))
res=c(3,4,3,4,3,4,1,2,1,2,1,2)
desired=data.frame(x1,x2,x3,res)
df
tabledf
desired


I realise that this is probably quite simple to do, I am just struggling to get my head around it! Help much appreciated in advance.

Cheers,

Simon

--------------------------------
Simon O'Hanlon BSc, MSc
Department of Infectious Disease Epidemiology
Imperial College London
St. Mary's Hospital
London
W2 1PG