在 R 中按组抽取多个大小为 n 的 k 个样本

Question

I have a dataset that looks like this:

group=rep(1:4,each=100)
values=round(runif(400,25,350),0)

data<-data.frame(values,group)

Each group is comprised by 100 observations (values).

For each group, I would take 20 random samples without replacement and varying sampling size starting from 10 and increasing by 5 up to 95.

Thus for each group I want 20 samples with size=10, 20 samples with size=15....20 samples with size=95.

Any idea on how to do it using some tidyverse solution?

At the moment I did this:

data %>% 
  group_by(group) %>% 
  nest() %>% 
  mutate(v=map(data,~rep_sample_n(.,size=10,replace=FALSE,reps=20))) %>% 
  unnest(v)

It seems correctly replicate 20 times a sample with size=10, but still I need to change the size...

Thanks.

Answer 1

You could create a sequence of sample sizes, wrap your group_by/nest/etc dude into a For loop, then add each new sample to a list.

Notice how the size argument in ~rep_sample_n is now sizes[i] rather than a fixed number.

sizes <- seq(10,95,by=5)

sample_list <- list()

for (i in 1:length(sizes)){

  new_data <- data %>% 
    group_by(group) %>% 
    nest() %>% 
    mutate(v=map(data,~rep_sample_n(.,size=sizes[i],replace=FALSE,reps=20))) %>% 
    unnest(v)
  
  sample_list[i] <- new_data

}

I am suggesting a for loop instead of lapply() , as it makes more sense to me and this application doesn't take much time anyway.