[Rd] reshape scaling with large numbers of times/rows

[Mitch Skinner]

On Thu, 2006-08-24 at 08:57 -0400, Gabor Grothendieck wrote:
> If your Z in reality is not naturally numeric try representing it as a
> factor and using
> the numeric levels as your numbers and then put the level labels back on:
> 
> m <- n <- 5
> DF <- data.frame(X = gl(m*n, 1), Y = gl(m, n), Z = letters[1:25])
> Zn <- as.numeric(DF$Z)
> system.time(w1 <- reshape(DF, timevar = "X", idvar = "Y", dir = "wide"))
> system.time({Zn <- as.numeric(DF$Z)
>    w2 <- xtabs(Zn ~ Y + X, DF)
>    w2[w2 > 0] <- levels(DF$Z)[w2]
>    w2[w2 == 0] <- NA
> })

This is pretty slick, thanks.  It looks like it works for me.  For the
archives, this is how I got back to a data frame (as.data.frame(w2)
gives me a long version again):

> m <- 4500
> n <- 70
> DF <- data.frame(X = gl(m, n), Y = 1:n, Z = letters[1:25])
> system.time({Zn <- as.numeric(DF$Z)
+    w2 <- xtabs(Zn ~ Y + X, DF)
+    w2[w2 > 0] <- levels(DF$Z)[w2]
+    w2[w2 == 0] <- NA
+    WDF <- data.frame(Y=dimnames(w2)$Y)
+    for (col in dimnames(w2)$X) { WDF[col]=w2[,col] }
+ })
[1] 131.888   1.240 135.945   0.000   0.000
> dim(WDF)
[1]   70 4501

I'll have to look; maybe I can just use w2 as is.  Next time I guess
I'll try R-help first.

Thanks again,
Mitch