r - 按条件将数据框的一列与另一列分开

Question

我有一个包含 2 列的数据框，如下所示:

cond  val
1      5
2      18
2      18
2      18
3      30
3      30

我想以这种方式更改 val 中的值:

   cond  val
    1      5   # 5 = 5/1  (only "1" in cond column)
    2      6   # 6 = 18/3 (there are three "2" in cond column)
    2      6
    2      6
    3      15  # 15 = 30/2  
    3      15

如何实现这一目标？

Answer 1

基础 R 解决方案:

# method 1:
mydf$val <- ave(mydf$val, mydf$cond, FUN = function(x) x = x/length(x))
# method 2:
mydf <- transform(mydf, val = ave(val, cond, FUN = function(x) x = x/length(x)))

给出:

  cond val
1    1   5
2    2   6
3    2   6
4    2   6
5    3  15
6    3  15