sorting a data frame on a numeric variable conditioned on a factor variable

sort_tapply.R

DF1 = DF[order(DF$factor_var, -xtfrm(DF$numeric_var)),]
DF1$idx = sequence(rle(as.character(DF1$factor_var))$lengths)


$> # e.g., sort a data frame based on 'price' (numeric variable)
$> # 'grouped by' the levels of 'color' (factor, or discrete variable)

$> data(diamonds, package="ggplot2")

$> DF = diamonds[1:1000,]   # first thousand rows of DF

$> DF1 = DF[order(DF$color, -xtfrm(DF$price)),]

$> DF1$idx = sequence(rle(as.character(DF1$color))$lengths)