[R] How to group by then count?

Monnand monnand at gmail.com
Sun Jan 4 10:02:55 CET 2015

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!


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