R help - Jan 2012 - summary per group

Hello,

I know that it'll be quite easy to do what I want but somehow I am lost as I
am new to R. I want to get summary results arranged by groups. In detail
I'd like get the number (levels) of Species per Family like for this
dataset:

SPEC <-
factor(c("a","a","b","b","c","c","c","d","e","e","e","e"))
FAM <-
factor(c("A","A","A","A","B","B","B","C","C","C","C","C"))
df <- data.frame(SPEC,FAM)

I tried tapply(SPEC, FAM, nlevels).. but it is not the result I am looking
for...

What is the easiest way to do that? Do I have to rearrange the dataset?

Best regards and Happy New Year!

Johannes

--

Hi
> 
> Hello,
> 
> I know that it'll be quite easy to do what I want but somehow I am lost
as
> I am new to R. I want to get summary results arranged by groups. In 
detail
> I'd like get the number (levels) of Species per Family like for this 
dataset:
> 
> SPEC <-
factor(c("a","a","b","b","c","c","c","d","e","e","e","e"))
> FAM <-
factor(c("A","A","A","A","B","B","B","C","C","C","C","C"))
> df <- data.frame(SPEC,FAM)
> 
> I tried tapply(SPEC, FAM, nlevels).. but it is not the result I am 
looking for...
> 
> What is the easiest way to do that? Do I have to rearrange the dataset?
To do what? Do you want number of unique entries within each level of FAM? 
If yes

sapply(tapply(SPEC, FAM, unique), length)

can do this.

Regards
Petr

> 
> Best regards and Happy New Year!
> 
> Johannes
> 
> --
> 
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.

Hi,

On Mon, Jan 2, 2012 at 8:08 AM, Johannes Radinger <JRadinger at gmx.at>
wrote:
> Hello,
>
> I know that it'll be quite easy to do what I want but somehow I am lost
as I am new to R. I want to get summary results arranged by groups. In detail
> I'd like get the number (levels) of Species per Family like for this
dataset:
>
> SPEC <-
factor(c("a","a","b","b","c","c","c","d","e","e","e","e"))
> FAM <-
factor(c("A","A","A","A","B","B","B","C","C","C","C","C"))
> df <- data.frame(SPEC,FAM)
>
> I tried tapply(SPEC, FAM, nlevels).. but it is not the result I am looking
for...
>
> What is the easiest way to do that? Do I have to rearrange the dataset?
nlevels() gives the number of levels defined, not the number of levels that have
members, so for your example will always be 5.
> with(df, aggregate(SPEC, by=list(FAM), nlevels))
  Group.1 x
1       A 5
2       B 5
3       C 5

You could drop the unused levels before checking:
> with(df, aggregate(SPEC, by=list(FAM), function(x)nlevels(factor(x))))
  Group.1 x
1       A 2
2       B 1
3       C 2

Or actually get a list of which ones are used:
> with(df, table(FAM, SPEC))
   SPEC
FAM a b c d e
  A 2 2 0 0 0
  B 0 0 3 0 0
  C 0 0 0 1 4

Sarah

-- 
Sarah Goslee
http://www.functionaldiversity.org