根据 R 中的唯一列值创建 data.frame？

Question

我有一个 data.frame 的观察结果，其中包含元数据列，我想创建一个新的 data.frame，其中包含相同的列，但每行代表每个列值的唯一组合。这是一个例子：

# what I have
df <- data.frame("Color" = c("Red", "Blue", "Green", "Green"), 
                 "Size" = c("Large", "Large", "Large", "Small"), 
                 "Value" = c(0, 1, 1, 1))
> df
  Color  Size Value
1   Red Large     0
2  Blue Large     1
3 Green Large     1
4 Green Small     1

# what I want
ideal_df <- data.frame("Color" = c("Red", "Red", "Red", "Red", "Blue", "Blue", "Blue", "Blue", "Green", "Green", "Green", "Green"), 
                       "Size" = c("Large", "Large", "Small", "Small", "Large", "Large", "Small", "Small", "Large", "Large", "Small", "Small"), 
                       "Value" = c(0,1,0,1,0,1,0,1,0,1,0,1))
> ideal_df
   Color  Size Value
1    Red Large     0
2    Red Large     1
3    Red Small     0
4    Red Small     1
5   Blue Large     0
6   Blue Large     1
7   Blue Small     0
8   Blue Small     1
9  Green Large     0
10 Green Large     1
11 Green Small     0
12 Green Small     1

我试过使用 for 循环，但我的数据比这个例子大得多，它挂起。我试图搜索这个问题，但找不到类似的东西。如果这个问题已经得到解答，我很乐意查看其他主题！谢谢你的时间。

Answer 1

这是 tidyr 包中 expand() 的工作：

library(tidyr)

new_df <- df %>% expand(Color, Size, Value)

Answer 2

只是添加一个base R解决方案：

new_df <- expand.grid(Color = unique(df$Color)
                   , Size = unique(df$Size)
                   , Value = unique(df$Value))

如果性能是一个问题，这里有一个基准比较：

sandy <- function(){
  expand(df, Color, Size, Value)
}

cj <- function(){
  expand.grid(Color = unique(df$Color)
              , Size = unique(df$Size)
              , Value = unique(df$Value))
}

library(microbenchmark)
microbenchmark(sandy(), cj())
Unit: microseconds
    expr      min       lq      mean   median       uq      max neval
 sandy() 1382.524 1494.675 1693.1749 1562.084 1736.524 7352.916   100
    cj()  138.914  152.746  204.8588  173.321  191.910 2889.398   100

根据 R 中的唯一列值创建 data.frame？

Create data.frame based on unique column values in R?

r

unique

dataframe