SAS在R中转置等效的列表

Data:

数据：

  set.seed(0)
    date <- rep(1:4,3)
    N <- length(date)
    A <- rnorm(N)
    B <- rnorm(N)
    C <- rnorm(N)
    mydata <- data.frame(date, A, B, C)

   date            A          B           C
1     1  1.262954285 -1.1476570 -0.05710677
2     2 -0.326233361 -0.2894616  0.50360797
3     3  1.329799263 -0.2992151  1.08576936
4     4  1.272429321 -0.4115108 -0.69095384
5     1  0.414641434  0.2522234 -1.28459935
6     2 -1.539950042 -0.8919211  0.04672617
7     3 -0.928567035  0.4356833 -0.23570656
8     4 -0.294720447 -1.2375384 -0.54288826
9     1 -0.005767173 -0.2242679 -0.43331032
10    2  2.404653389  0.3773956 -0.64947165
  set.seed(0)
    date <- rep(1:4