[R] count ties after rank?

[Peter Langfelder]

On Mon, Nov 21, 2011 at 11:36 AM, Hao, Zhaozhe <haozhaozhe at ou.edu> wrote:
> Hello!
>
>    I need to use Kruskal-Wallis test and post-hoc test (Dunn's test) for my data. But when I searched around, I only found this function: kruskal.test. But nothing for Dunn's test.
>
>    So I started to write one myself.  But  I do not know how to count ties in the data frame. I can use for loops but it seems long and unnecessary since the rank function actually knows the ties. So can anyone give me a hint on how I can "count" the number of ties?
>

If you just need the overall number of ties in a vector (say x), you
can get it by

nTies = length(x) - length(unique(x))

This will not work if missing data are present, so you will have to
remove those first.

HTH,

Peter