有放回的样本，但限制每个成员的最大抽取频率

Question

是否可以将 R 中的 sample 函数扩展为不 return 超过说 replace = TRUE 时相同元素的 2 个？

假设我有一个列表：

l = c(1,1,2,3,4,5)

要对 3 个元素进行替换采样，我会这样做：

sample(l, 3, replace = TRUE)

有没有办法限制它的输出，以便最多只能 return 编辑 2 个相同的元素？所以(1,1,2)或(1,3,3)是允许的，但(1,1,1)或(3,3,3)是被排除的？

Answer 1

set.seed(0)

基本思想是将有放回抽样转换为无放回抽样。

ll <- unique(l)          ## unique values
#[1] 1 2 3 4 5
pool <- rep.int(ll, 2)   ## replicate each unique so they each appear twice
#[1] 1 2 3 4 5 1 2 3 4 5
sample(pool, 3)          ## draw 3 samples without replacement
#[1] 4 3 5

## replicate it a few times
## each column is a sample after out "simplification" by `replicate`
replicate(5, sample(pool, 3))
#     [,1] [,2] [,3] [,4] [,5]
#[1,]    1    4    2    2    3
#[2,]    4    5    1    2    5
#[3,]    2    1    2    4    1

如果您希望不同的值出现最多不同的次数，我们可以这样做

pool <- rep.int(ll, c(2, 3, 3, 4, 1))
#[1] 1 1 2 2 2 3 3 3 4 4 4 4 5

## draw 9 samples; replicate 5 times
oo <- replicate(5, sample(pool, 9))
#      [,1] [,2] [,3] [,4] [,5]
# [1,]    5    1    4    3    2
# [2,]    2    2    4    4    1
# [3,]    4    4    1    1    1
# [4,]    4    2    3    2    5
# [5,]    1    4    2    5    2
# [6,]    3    4    3    3    3
# [7,]    1    4    2    2    2
# [8,]    4    1    4    3    3
# [9,]    3    3    2    2    4

我们可以在每一列上调用tabulate来计算1, 2, 3, 4, 5的频率：

## set `nbins` in `tabulate` so frequency table of each column has the same length
apply(oo, 2L, tabulate, nbins = 5)
#     [,1] [,2] [,3] [,4] [,5]
#[1,]    2    2    1    1    2
#[2,]    1    2    3    3    3
#[3,]    2    1    2    3    2
#[4,]    3    4    3    1    1
#[5,]    1    0    0    1    1

所有列中的计数都满足我们设置的频率上限c(2, 3, 3, 4, 1)。

Would you explain the difference between rep and rep.int?

rep.int 不是 rep 的 "integer" 方法。它只是一个更快的原始函数，功能比 rep 少。您可以从文档页面 ?rep.

获取 rep、rep.int 和 rep_len 的更多详细信息

有放回的样本，但限制每个成员的最大抽取频率

sample with replacement but constrain the max frequency of each member to be drawn

random

r

sample