这是 reshape2 的 dcast() 中的 which.min? [英] which.min within reshape2's dcast()?

问题描述

我想提取每个建筑月份组合中 var1 最小值对应的 var2 值.这是我的(假)数据集:

I would like to extract the value of var2 that corresponds to the minimum value of var1 in each building-month combination. Here's my (fake) data set:

 head(mydata)

 #  building month      var1     var2
 #1        A     1 -26.96333 376.9633
 #2        A     1 165.38759 317.3993
 #3        A     1  47.46345 271.0137
 #4        A     2  73.47784 294.8171
 #5        A     2 107.80130 371.7668
 #6        A     2  10.16384 308.7975

可重现的代码:

## create fake data set:
set.seed(142)
mydata1 = data.frame(building = rep(LETTERS[1:5],6),month = sort(rep(1:6,5)),var1=rnorm(30,50,35),var2 = runif(30,200,400))
mydata2 = data.frame(building = rep(LETTERS[1:5],6),month = sort(rep(1:6,5)),var1=rnorm(30,60,35),var2 = runif(30,150,400))
mydata3 = data.frame(building = rep(LETTERS[1:5],6),month = sort(rep(1:6,5)),var1=rnorm(30,40,35),var2 = runif(30,250,400))
mydata = rbind(mydata1,mydata2,mydata3)
mydata = mydata[ order(mydata[,"building"], mydata[,"month"]), ]
row.names(mydata) = 1:nrow(mydata)

## here is how I pull the minimum value of v1 for each building-month combination:
require(reshape2)
m1 = melt(mydata, id.var=1:2)
d1 = dcast(m1, building ~ month, function(x) min(max(x,0), na.rm=T),
           subset = .(variable == "var1"))

这会为每个构建月组合提取 var1 的最小值...

This pulls out the minimum value of var1 for each building-month combo...

head(d1)

#  building         1         2        3         4         5         6
#1        A 165.38759 107.80130 93.32816  73.23279  98.55546 107.58780
#2        B  92.08704  98.94959 57.79610  94.10530  80.86883  99.75983
#3        C  93.38284 100.13564 52.26178  62.37837  91.98839  97.44797
#4        D  82.43440  72.43868 66.83636 105.46263 133.02281  94.56457
#5        E  70.09756  61.44406 30.78444  68.24334  94.35605  61.60610

然而，我想要的是一个完全设置为 d1 的数据框，而是显示 var2 的值，该值对应于为 var1 拉取的最小值(显示在 d1 以上).我的直觉告诉我它应该是 which.min() 的变体，但还没有让它与 dcast() 或 ddply()<一起使用/代码>.任何帮助表示赞赏！

However, what I want is a data frame set up exactly as d1 that instead shows the value of var2 that corresponds to the minimum value pulled for var1 (shown in d1 above). My gut tells me it should be a variation on which.min(), but haven't gotten this to work with dcast() or ddply(). Any help is appreciated!

推荐答案

可能一步就能搞定，但我对 plyr 比 reshape2 更熟悉，

It may be possible in one step, but I'm more familiar with plyr than reshape2,

dcast(ddply(mydata, .(building, month), summarize, value = var2[which.min(var1)]), 
      building ~ month)

这篇关于这是 reshape2 的 dcast() 中的 which.min?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！