R help - Nov 2011 - count ties after rank?

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?

    Many thanks.

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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

On Nov 21, 2011, at 2:36 PM, Hao, Zhaozhe wrote:
> Hello!
>
>    I need to use Kruskal-Wallis test and post-hoc test (Dunn's test)  
> for my data. But when I searched around,
"Searching around" is a bit vague as a search strategy:

Try :kruskal dunn" at the location that RSiteSearch gets you to:

http://search.r-project.org/cgi-bin/namazu.cgi?query=kruskal+Dunn&max=100&result=normal&sort=score&idxname=functions&idxname=Rhelp08&idxname=Rhelp10&idxname=Rhelp02

Or in its default settings:

http://search.r-project.org/cgi-bin/namazu.cgi?query=kruskal+Dunn&max=100&result=normal&sort=score&idxname=functions&idxname=vignettes&idxname=views

> I only found this function: kruskal.test. But nothing for Dunn's test.
>
>    So I started to write one myself.
You are perhaps referring to what others are callng the  Nemenyi- 
Damico-Wolfe-Dunn test. See the last example in the entry that ? 
kruskal_test would have gotten you... had you known where it was.

install.packages("coin")
require(coin)
help("LocationTests")

>  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?
>
>    Many thanks.

-- 
David Winsemius, MD
West Hartford, CT