[R] contingency table on data frame

[Domenico Vistocco]

Karin Lagesen wrote:
> I am sorry if this is a faq or tutorial somewhere, but I am unable to
> solve this one.
>
> What I am looking for is a count of how many different
> categories(numbers in this case) that appears for a given factor.
>
> Example:
>
>   
>> l <- c("Yes", "No", "Perhaps")
>> x <- factor( sample(l, 10, replace=T), levels=l )
>> m <- c(1:5)
>> y <- factor( sample(m, 10, replace=T), levels=m )
>> z = c(1:10)
>> my_df = data.frame("Z" = z, "Y"= y, "X" = x)
>> my_df
>>     
>     Z Y       X
> 1   1 4     Yes
> 2   2 1      No
> 3   3 2 Perhaps
> 4   4 3     Yes
> 5   5 4      No
> 6   6 5      No
> 7   7 1     Yes
> 8   8 4 Perhaps
> 9   9 4     Yes
> 10 10 2 Perhaps
>   
>
> I am now looking for a table that will give me this:
>
> Yes      3       # Yes has these ys: 4,3,1,4, two are the same, ergo 3
> No       3       # No has these ys: 1,4,5
> Perhaps  2       # Perhaps has these ys: 2,4,2
>   
Maybe:
apply(table(my_df$X,my_df$Y),1,function(x) sum(x!=0))

domenico
> My dataframe has lots of other colums too, but I only want this
> information out.
>
>
> Thankyou for your help!
>
> Karin
>