[R] Conditional Loop For Data Frame Columns

[Rui Barradas]

P.S.

If you want to use your function, revised, it may be a good idea: it's
faster


#write indexed mean function
meanfun <- function(x, inx, na.rm=FALSE) {
	meanSD <- matrix(0, nrow=length(levels(inx)), ncol=length(3:ncol(x)))
	for(i in 3:ncol(x)) {
		meanSD[, i - 2] <- tapply(x[,i], ID, FUN=mean, na.rm=na.rm)}
	return(meanSD)
}


# apply function to data
meanfun(SD, ID, T)

# compare results
meanfun(SD, ID, T)[, (nc-9):(nc-3)]
aggregate(SD[, 3:nc], by=list(ID), mean, na.rm=TRUE)[, (nc-8):(nc-2)]


# now make it bigger for timming
SD <- rbind(SD, SD, SD, SD, SD, SD, SD, SD)
SD <- rbind(SD, SD, SD, SD, SD, SD, SD, SD)
SD <- rbind(SD, SD, SD, SD, SD, SD, SD, SD)
SD <- rbind(SD, SD, SD, SD, SD, SD, SD, SD)
dim(SD)

ID <- SD[ ,2]
system.time(aggregate(SD[, 3:nc], by=list(ID), mean))
   user  system elapsed 
   9.72    0.01    9.75

system.time(meanfun(SD, ID))
   user  system elapsed 
   3.21    0.03    3.24

Rui Barradas


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