[R] Dataframe of factors transform speed?

[Charles C. Berry]

On Thu, 19 Jul 2007, Latchezar Dimitrov wrote:

> Hello,
>
> This is a speed question. I have a dataframe genoT:
>
>> dim(genoT)
> [1]   1002 238304

It looks like these are all numeric originally. Handling these as a
vector or matrix will speed things up a bit. You can then stitch
together a data.frame:

# simulate: 
#       genoT.names <- scan('data.file, what='a', nlines=1, <etc> ) 
# 	genoT <- scan('data.file',skip=1)
#
>
> genoT <- sample(0:2, 240000*1002, repl=T)
> t1 <- proc.time()
> genoT <- factor(genoT,0:2,c("AA","AB","BB"))
> dim(genoT) <- c(1002,240000)
> genoT.list <- lapply(1:240000, function(x) genoT[,x])
> # simulate: names(genoT.list) <- genoT.names :
> names(genoT.list) <- make.names(1:240000)
> class(genoT.list) <- "data.frame"
> row.names(genoT.list) <- 1:1002
> proc.time()-t1
    user  system elapsed
  20.978   2.036  49.714
>

Most of the _elapsed_ time is due to lags in copy-and-paste-ing in the 
commands.

HTH,

Chuck
>
>> str(genoT)
> 'data.frame':   1002 obs. of  238304 variables:
> $ SNP_A.4261647: Factor w/ 3 levels "0","1","2": 3 3 3 3 3 3 3 3 3 3
> ...
> $ SNP_A.4261610: Factor w/ 3 levels "0","1","2": 1 1 3 3 1 1 1 2 2 2
> ...
> $ SNP_A.4261601: Factor w/ 3 levels "0","1","2": 1 1 1 1 1 1 1 1 1 1
> ...
> $ SNP_A.4261704: Factor w/ 3 levels "0","1","2": 3 3 3 3 3 3 3 3 3 3
> ...
> $ SNP_A.4261563: Factor w/ 3 levels "0","1","2": 3 1 2 1 2 3 2 3 3 1
> ...
> $ SNP_A.4261554: Factor w/ 3 levels "0","1","2": 1 1 NA 1 NA 2 1 1 2 1
> ...
> $ SNP_A.4261666: Factor w/ 3 levels "0","1","2": 1 1 2 1 1 1 1 1 1 2
> ...
> $ SNP_A.4261634: Factor w/ 3 levels "0","1","2": 3 3 2 3 3 3 3 3 3 2
> ...
> $ SNP_A.4261656: Factor w/ 3 levels "0","1","2": 1 1 2 1 1 1 1 1 1 2
> ...
> $ SNP_A.4261637: Factor w/ 3 levels "0","1","2": 1 3 2 3 2 1 2 1 1 3
> ...
> $ SNP_A.4261597: Factor w/ 3 levels "AA","AB","BB": 2 2 3 3 3 2 1 2 2 3
> ...
> $ SNP_A.4261659: Factor w/ 3 levels "AA","AB","BB": 3 3 3 3 3 3 3 3 3 3
> ...
> $ SNP_A.4261594: Factor w/ 3 levels "AA","AB","BB": 2 2 2 1 1 1 2 2 2 2
> ...
> $ SNP_A.4261698: Factor w/ 2 levels "AA","AB": 1 1 1 1 1 1 1 1 1 1 ...
> $ SNP_A.4261538: Factor w/ 3 levels "AA","AB","BB": 2 3 2 2 3 2 2 1 1 2
> ...
> $ SNP_A.4261621: Factor w/ 3 levels "AA","AB","BB": 1 1 1 1 1 1 1 1 1 1
> ...
> $ SNP_A.4261553: Factor w/ 3 levels "AA","AB","BB": 1 1 2 1 1 1 1 1 1 1
> ...
> $ SNP_A.4261528: Factor w/ 2 levels "AA","AB": 1 1 1 1 1 1 1 1 1 1 ...
> $ SNP_A.4261579: Factor w/ 3 levels "AA","AB","BB": 1 1 1 1 1 2 1 1 1 2
> ...
> $ SNP_A.4261513: Factor w/ 3 levels "AA","AB","BB": 2 1 2 2 2 NA 1 NA 2
> 1 ...
> $ SNP_A.4261532: Factor w/ 3 levels "AA","AB","BB": 1 2 2 1 1 1 3 1 1 1
> ...
> $ SNP_A.4261600: Factor w/ 2 levels "AB","BB": 2 2 2 2 2 2 2 2 2 2 ...
> $ SNP_A.4261706: Factor w/ 2 levels "AA","BB": 1 1 1 1 1 1 1 1 1 1 ...
> $ SNP_A.4261575: Factor w/ 3 levels "AA","AB","BB": 1 1 1 1 1 1 1 2 2 1
> ...
>
> Its columns are factors with different number of levels (from 1 to 3 -
> that's what I got from read.table, i.e., it dropped missing levels). I
> want to convert it to uniform factors with 3 levels. The 1st 10 rows
> above show already converted columns and the rest are not yet converted.
> Here's my attempt wich is a complete failure as speed:
>
>> system.time(
> +     for(j in 1:(10         )){ #-- this is to try 1st 10 cols and
> measure the time, it otherwise is ncol(genoT) instead of 10
>
> +        gt<-genoT[[j]]          #-- this is to avoid 2D indices
> +        for(l in 1:length(gt at levels)){
> +          levels(gt)[l] <- switch(gt at levels[l],AA="0",AB="1",BB="2")
> #-- convert levels to "0","1", or "2"
> +          genoT[[j]]<-factor(gt,levels=0:2)   #-- make a 3-level factor
> and put it back
> +        }
> +     }
> + )
> [1] 785.085   4.358 789.454   0.000   0.000
>
> 789s for 10 columns only!
>
> To me it seems like replacing 10 x 3 levels and then making a factor of
> 1002 element vector x 10 is a "negligible" amount of operations needed.
>
> So, what's wrong with me? Any idea how to accelerate significantly the
> transformation or (to go to the very beginning) to make read.table use a
> fixed set of levels ("AA","AB", and "BB") and not to drop any (missing)
> level?
>
> R-devel_2006-08-26, Sun Solaris 10 OS - x86 64-bit
>
> The machine is with 32G RAM and AMD Opteron 285 (2.? GHz) so it's not
> it.
>
> Thank you very much for the help,
>
> Latchezar Dimitrov,
> Analyst/Programmer IV,
> Wake Forest University School of Medicine,
> Winston-Salem, North Carolina, USA
>
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>

Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901