[R] data.frame <- table

[Z. Todd Taylor]

Arnoldsson <Goran.Arnoldsson at stat.umu.se> wrote:

> I have an 8-dimensional contingency table (640 cells) produced by the
> table function. Which is the easiest method to transform the table to a
> data frame with 8 factors and a 9th column for the frequencies (for
> further log-linear modelling)? Perhaps there is a function in a package
> somewhere in R-space?

Here's a function I've used for years, mostly in S (it's a simple
wrapper around expand.grid):

   dfify <- function(arr, value.name = "value", dn.names = names(dimnames(arr))) {
   
      Version <- "$Id: dfify.sfun,v 1.1 1995/10/09 16:06:12 d3a061 Exp $"
      dn <- dimnames(arr <- as.array(arr))
      if(is.null(dn))
         stop("Can't data-frame-ify an array without dimnames")
      names(dn) <- dn.names
      ans <- cbind(expand.grid(dn), as.vector(arr))
      names(ans)[ncol(ans)] <- value.name
      ans
   }

The name is short for "data-frame-i-fy".

For your example, assuming your multi-way array has proper
dimnames, you'd just do:

   my.data.frame <- dfify(my.array, value.name="frequency")

--Todd
-- 
Z. Todd Taylor
Pacific Northwest National Laboratory
Todd.Taylor at pnl.gov
Why is it unable and inability, not inable and unability?
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