包含每个因子至少一个实例的随机子集 [英] Random subset containing at least one instance of each factor

问题描述

让我们定义一个3列10行的 data.frame df.第三列是类，前两个是一些变量.

Let's define a data.framedf with 3 columns and 10 rows. The third column is the class and the two first some variables.

var1 <- rnorm(10)
var2 <- rnorm(10,2)
class<- as.factor(c(1,2,3,1,2,1,2,1,3,3))
df   <- data.frame(var1=var1,var2=var2,class=class)

如何将 df 随机分为两个子集，以使sub.df1和sub.df2至少具有每个类的一个实例?

How to randomly subset df in two subsets so that sub.df1 and sub.df2 have at least one instance of each class?

推荐答案

这有效:

set.seed(123)
partition <- function(x, n = 2) sample(c(1:n, sample(1:n, length(x) - n, TRUE)))
split(df, as.integer(ave(df$class, df$class, FUN = partition)))

# $`1`
#          var1      var2 class
# 4   1.6674610 3.3886789     1
# 7  -0.2245588 0.8284845     2
# 8  -1.1481185 4.1586492     1
# 10 -0.4712463 3.1846324     3
# 
# $`2`
#         var1       var2 class
# 1  0.9884264  3.3487054     1
# 2 -0.1549679 -0.5815586     2
# 3  1.4484692  0.3521933     3
# 5  0.5454097  2.0405363     2
# 6  1.0971626  0.6410492     1
# 9 -1.3042283  3.3235418     3

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