[R] summary per group

[Petr PIKAL]

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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