Sort data frame column by factor

Question

Supose I have a data frame with 3 columns (name, y, sex) where name is character, y is a numeric value and <

Answer 1

It sounds to me like you're trying to order by score within the males and females and return a combined data frame of sorted males and sorted females.

You are right that by(score, score$sex, function(x) x[order(x$y),]) returns a list of sorted data frames, one for male and one for female. You can use do.call with the rbind function to combine these data frames into a single final data frame:

do.call(rbind, by(score, score$sex, function(x) x[order(x$y),]))
#           x         y sex
# F.5    EMMA  7.526866   F
# F.9  VIOLET  8.182407   F
# F.3   SUSAN  9.677511   F
# M.4   LARRY  6.929395   M
# M.8    MATT  7.970015   M
# M.7     TIM  8.297137   M
# M.6 LEONARD  8.845588   M
# M.2     TOM  9.035948   M
# M.1    MARK 10.082314   M