Apply a function to dataframe subsetted by all possible combinations of categorical variables

Question

An example dataframe with categorical variables catA, catB, and catC. Obs is some observed value.

catA <- rep(factor(c(\"a\",\"b\",\"c\")), length.out=10         


        

Answer 1

An alternative approach, one function to get all combinations of variables and another to apply a function over all subsets. The combinations function was stolen from another post...

## return all combinations of vector up to maximum length n
multicombn <- function(dat, n) {
    unlist(lapply(1:n, function(x) combn(dat, x, simplify=F)), recursive=F)
}

For allsubs, vars is of form c("catA","catB","catC"), out.name = "mean". func needs to be written in form that ddply would take,

func=function(x) mean(x$obs, na.rm=TRUE)

library(plyr)
allsubs <- function(indat, vars, func=NULL, out.name=NULL) {
    results <- data.frame()
    nvars <- rev(multicombn(vars,length(vars)))
    for(i in 1:length(nvars)) {
        results <-
            rbind.fill(results, ddply(indat, unlist(nvars[i]), func))
    }
    if(!missing(out.name)) names(results)[length(vars)+1] <- out.name
    results
}

One difference between this answer and shwaund's, this does not return rows for empty subsets, so no NAs in results column.

allsubs(dat, c("catA","catB","catc"), func, out.name="mean")
> head(allsubs(dat, vars, func, out.name = "mean"),20)
   catA catB catC     mean
1     a    1    d 56.65909
2     a    2    d 54.98116
3     a    3    d 37.52655
4     a    4    d 58.29034
5     b    1    e 52.88945
6     b    2    e 50.43122
7     b    3    e 52.57115
8     b    4    e 59.45348
9     c    1    f 52.41637
10    c    2    f 34.58122
11    c    3    f 46.80256
12    c    4    f 51.58668
13     1    d 56.65909
14     1    e 52.88945
15     1    f 52.41637
16     2    d 54.98116
17     2    e 50.43122
18     2    f 34.58122
19     3    d 37.52655
20     3    e 52.57115