[R] which is the fastest way to make data.frame out of a three-dimensional array?

[Hans Ekbrand]

First, thank you both Bert and Petr for your excellent answers. 

Berts solution seems somewhat faster, and Petrs is - in my opion at
least - slightly more elegant.

> foo <- rnorm(36 * 150 * 170)
> dim(foo) <- c(36, 150, 170)
> n <- dim(foo)
> 
> system.time(my.df <- data.frame(dat = as.vector(foo),
+                     dim1 = rep(seq_len(n[1]), n[2]*n[3]),
+                     dim2 = rep(rep(seq_len(n[2]), e=n[1]), n[3]),
+                     dim3 = rep(seq_len(n[3]), e = n[1]*n[2])))
   user  system elapsed 
  0.932   0.156   1.090 
> 
> system.time(my.df <- cbind(temp=c(foo), expand.grid(dim1=1:n[1], dim2=1:n[2], dim3=1:n[3])))
   user  system elapsed 
  0.980   0.252   1.244 
> 

-- 
Hans Ekbrand (http://sociologi.cjb.net) <hans at sociologi.cjb.net>