随机抽取一组，得到一个平衡组

Question

这是我的数据帧：

data<- 
ID     Group    Modules
1      Male      Physics
1      Male      Chemistry
2      Female    Biology
2      Female    Physics
2      Female    Chemistry
3      Male      Physics
3      Male      Biology
3      Male      Chemistry
4      Male      Physics
4      Male      Biology
4      Male      Chemistry
5      Male      Physics
5      Male      Biology
5      Male      Chemistry
6      Male      Physics
6      Male      Biology
6      Male      Chemistry
7      Female    Physics
7      Female    Biology
8      Female    Chemistry
8      Male      Physics
8      Male      Biology
9      Male      Chemistry
9      Male      Physics
10      Male      Biology
10      Male      Chemistry
10      Male      Physics
11      Male      Biology
11      Male      Chemistry
11      Male      Physics
12      Female    Biology
12      Female    Chemistry

上述数据中男性(n=9(多于女性(n=3(。我想随机选择3只雄性而不重新交配，所以我最终会得到3只雄性和3只雌性。我也想保留重复的ID，所以我担心的结果是：

newdata<- 
ID     Group    Modules
1      Male      Physics
1      Male      Chemistry
2      Female    Biology
2      Female    Physics
2      Female    Chemistry
3      Male      Physics
3      Male      Biology
3      Male      Chemistry
7      Female    Physics
7      Female    Biology
7      Female    Chemistry
12     Female    Physics
12     Female    Biology
6      Male      Physics
6      Male      Biology
6      Male      Chemistry

下面是我的代码：

samples_per_group<-6
new data<-data%>% group_by(Group)%>%slice(sample(n(),min(sampples_per_group, n())))%>%ungroup()

当我尝试运行这个程序时，它选择了6个样本大小(每组3个(，但它只从每个参与者中提取一行，而不是返回该参与者的所有行。基本上，我想在每个组上选择3个id，而不管该id重复多少次。欢迎任何援助。谢谢

Answer 1

如果您想对ID进行采样，您需要获取ID并对其进行采样：

groups = data %>%
distinct(ID, Group) %>%
group_by(Group) %>%
summarize(group_size = n())
smallest_group = min(groups$group_size)
groups %>%
group_by(Group) %>%
sample_n(size = smallest_group) %>%
ungroup() %>%
left_join(data)

像上面这样的东西应该有效。很难在dplyr链中的组中获得单个数字——这是可行的——但我认为更简单的做法是打破管道并提取数字。我们按组采样3个(或多个(ID，然后连接回主数据以获得与这些ID对应的所有行。