[R] How to group by then count?

[Berend Hasselman]

> On 04-01-2015, at 10:02, Monnand <monnand at gmail.com> wrote:
> 
> Hi all,
> 
> I thought this was a very naive problem but I have not found any solution
> which is idiomatic to R.
> 
> The problem is like this:
> 
> Assuming we have vector of strings:
> x = c("1", "1", "2", "1", "5", "2")
> 
> We want to count number of appearance of each string. i.e. in vector x,
> string "1" appears 3 times; "2" appears twice and "5" appears once. Then I
> want to know which string is the majority. In this case, it is "1".
> 
> For imperative languages like C, C++ Java and python, I would use a hash
> table to count each strings where keys are the strings and values are the
> number of appearance. For functional languages like clojure, there're
> higher order functions like group-by.
> 
> However, for R, I can hardly find a good solution to this simple problem. I
> found a hash package, which implements hash table. However, installing a
> package simple for a hash table is really annoying for me. I did find
> aggregate and other functions which operates on data frames. But in my
> case, it is a simple vector. Converting it to a data frame may be not
> desirable. (Or is it?)
> 
> Could anyone suggest me an idiomatic way of doing such job in R? I would be
> appreciate for your help!
> 

Have a look at table:

?table

Berend