order - R Plyr - Ordering results from DDPLY? -

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does know slick way order results coming out of ddply summarise operation?

this i'm doing output ordered descending depth.

  ddims <- ddply(diamonds, .(color), summarise, depth = mean(depth), table = mean(table))   ddims <- ddims[order(-ddims$depth),]

with output...

> ddims   color    depth    table 7     j 61.88722 57.81239 6     61.84639 57.57728 5     h 61.83685 57.51781 4     g 61.75711 57.28863 1     d 61.69813 57.40459 3     f 61.69458 57.43354 2     e 61.66209 57.49120

not ugly, i'm hoping way nicely within ddply(). know how?

hadley's ggplot2 book has example ddply , subset it's not sorting output, selecting 2 smallest diamonds per group.

ddply(diamonds, .(color), subset, order(carat) <= 2)

i'll use occasion advertise bit data.table, faster run , (in perception) @ least elegant write:

library(data.table) ddims <- data.table(diamonds) system.time(ddims <- ddims[, list(depth=mean(depth), table=mean(table)), by=color][order(depth)])     user  system elapsed    0.003   0.000   0.004

by contrast, without ordering, ddply code takes 30 times longer:

  user  system elapsed   0.106   0.010   0.119

with respect have hadley's excellent work, e.g. on ggplot2, , general awesomeness, must confess me, data.table entirely replaced ddply -- speed reasons.


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