R Plyr-DDPLY的订购结果? [英] R Plyr - Ordering results from DDPLY?

问题描述

有人知道一种巧妙的方法来排序来自ddply摘要操作的结果吗?

Does anyone know a slick way to order the results coming out of a ddply summarise operation?

这是我要使输出按降序排序的操作.

This is what I'm doing to get the output ordered by descending depth.

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

有输出...

> ddims
  color    depth    table
7     J 61.88722 57.81239
6     I 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

不太丑陋，但是我希望在ddply()中很好地做到这一点.有人知道吗?

Not too ugly, but I'm hoping for a way do it nicely within ddply(). Anyone know how?

哈德利(Hadley)的ggplot2书使用了ddply和subset的示例，但实际上并没有对输出进行排序，只是每组选择两个最小的菱形.

Hadley's ggplot2 book has this example for ddply and subset but it's not actually sorting the output, just selecting the two smallest diamonds per group.

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

推荐答案

在这种情况下，我将为data.table做些广告，它运行得更快，并且(据我所知)至少写得很优雅:

I'll use this occasion to advertise a bit for data.table, which is faster to run and (in my perception) at least as elegant to 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 

通过对比，无需订购，您的ddply代码已经花费了30倍的时间:

By contrast, without ordering, your ddply code already takes 30 times longer:

  user  system elapsed 
 0.106   0.010   0.119

我对哈德利的出色作品表示敬意，例如在ggplot2上，以及一般的出色表现，我必须承认，对我来说，出于速度原因，data.table完全取代了ddply.

With all the respect I have for Hadley's excellent work, e.g. on ggplot2, and general awesomeness, I must confess that for me, data.table entirely replaced ddply -- for speed reasons.

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