[R] Aggregate drops empty subsets

[Sundar Dorai-Raj]

Andrew Robinson wrote:

> Greetings, R community.
> 
> I am trying to create a multi-dimensional contingency table suitable
> for analysis by glm() using the poisson family.  I have three factors,
> each with four levels, with some observed zeros.  I'm trying to use
> aggregate to construct my contingency table, but it drops empty
> subsets, so the zeros get lost.  I also tried tapply() but it doesn't
> carry over the main effects, just the interactions.  I also tried
> constructing a new factor from the interactions and merging it with
> the contingency table but then I lost the main effects.  
> 
> Very small example: from the following dataframe
> 
> burn  age
> 
> low   young
> high  old
> low   old
> low   young
> 
> I would want to distill
> 
> burn  age    burn.age     count
> low   young  low.young    2
> high  young  high.young   0
> low   old    low.old      1
> high  old    high.old     1
> 
> with a solution scaleable to many dimensions.
> 
> Is there any easy way to get around this problem?
> 
> Thanks for any suggestions,
> 
> Andrew

Hi Andrew,

How about:

ui <- data.frame(burn = c("low", "high", "low", "low"),
                  age = c("young", "old", "old", "young"),
                  junk = c("a", "a", "b", "b"))
ui2 <- do.call("table", ui)
ui3 <- expand.grid(dimnames(ui2))
ui3[paste(names(ui), collapse = ".")] <-
   do.call("paste", c(ui3, sep = "."))
ui3$count <- c(ui2)

I'm using R-1.9.0 on win2000.

--sundar