[R] Number of replications of a term

[Laetitia Marisa]

Hello,

Is there a simple and fast function that returns a vector of the number 
of replications for each object of a vector ?
For example :
I have a vector of IDs :
ids <- c( "ID1", "ID2", "ID2", "ID3", "ID3","ID3", "ID5")

 I want the function returns the following vector where each term is the 
number of replicates for the given id :
c( 1, 2, 2, 3,3,3,1 )

Of course I have a vector of more than 40 000 ID and the function I 
wrote (it orders my data and checks on ID:Name of the data if the next 
term is the same as the previous one (see below) ) is really slow 
(30minutes for 44290 terms). But I don't have time by now to write a C 
function.
Thanks a lot for your help,

Laetitia.



Here is the function I have written maybe I have done something not 
optimized :

repVector <- function(obj){

    # order IDName 
    ord <- gif.indexByIDName(obj)
    ordobj <- obj[ord,]

    nspots <- nrow(obj)
    # vector of spot replicates number           
    spotrep <- rep(NA, nspots )
   
    # function to get ID:Name for a given spot       
    spotidname <- function(ind){
            paste(ordobj$genes[ind, c("ID","Name") ], collapse=":")
    }

    spot <- 1   

    while( spot < nspots ){
        i<-1
        while( spotidname(spot) == spotidname(spot + i) ){            
       
            i <- i + 1
        }
       
        spotrep[spot : (spot + i-1)] <- i
        spot <- spot + i
        #cat("spot : ",spot,"\n")   
    }       
   
    obj$genes$spotrep <- spotrep[order(ord)]

    obj
               
}