将融化的数据帧重建回原始数据帧的更简单方法

如何重新创建 data.frame 我融化了 reshape2 ?

可复制示例

library(reshape2)
library(plyr)
data(iris)
df  <- melt(iris, id.vars="Species")
head(df)
  Species     variable value
1  setosa Sepal.Length   5.1
2  setosa Sepal.Length   4.9
3  setosa Sepal.Length   4.7
4  setosa Sepal.Length   4.6
5  setosa Sepal.Length   5.0
6  setosa Sepal.Length   5.4
# Great, I'd like to get the original iris back

我尝试过的 dcast

  dcast(df, Species~variable, value.var = "value")
    # should work but doesn't

临时解决方案

# This works but clearly it shouldn't be this hard.
ddply(df, .(Species), function(x) {
    Species <- unique(x$Species)
    x$id <- 1:dim(x)[1]
    x$Species <- NULL
    dat <- unstack(x, value~variable)
    dat$Species <- Species
    return(dat)
    })

我错过了什么?这是显而易见的,但我无法找出答案。我甚至可能以前为这里的其他人回答过这个问题。啊。