[R] Number of replications of a term

[Barry Rowlingson]

Laetitia Marisa wrote:
> 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 )

One-liner:

 > table(ids)[ids]
ids
ID1 ID2 ID2 ID3 ID3 ID3 ID5
   1   2   2   3   3   3   1

  'table(ids)' computes the counts, then the subscripting [ids] looks it 
all up.

  Now try it on your 40,000-long vector!

Barry