Using R's builtin ToothGrowth example dataset, this works:
ddply(ToothGrowth, .(supp,dose), function(df) mean(df$len))
But I would like to have the subsetting factors be variables, something like
factor1 = 'supp'
factor2 = 'dose'
ddply(ToothGrowth, .(factor1,factor2), function(df) mean(df$len))
That doesn't work. How should this be done?
I thought perhaps something like this:
factorCombo = paste('.(',factor1,',',factor2,')', sep='')
ddply(ToothGrowth, factorCombo, function(df) mean(df$len))
But it doesn't work either. I think I am close, but not sure the proper way to do it. I suppose the entire command could be put into a string, followed by an eval() call of the string, but hopefully is there a more elegant way?
Try:
x <- c("supp", "dose")
ddply(ToothGrowth, x, function(df) mean(df$len))
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