R模拟具有独特观察的样本

Question

我有一个包含两个分组变量和一个结果变量的数据集。我正在尝试从该数据集中模拟采样，但我只想要 either 变量中没有 ID 重复的样本。

我的数据结构如下，但有几百行：

structure(list(wteam = c("a", "a", "b", "c", "c", "d" ), week = c(1, 1, 1, 2, 2, 2), dif = c(0.649077088, 0.089812768, 0.173061282, 0.362544332, 0.459545808, 0.331745704)), row.names = c(NA, 6L), class = "data.frame")

我正在尝试从数据集中抽取 23 个观察值，这样 wteam 和 week 都不能在样本中重复。

我目前的方法效率极低：

    sims<-10
    weeks<-23
    outs<-as.data.frame(matrix(0,ncol = sims, nrow = weeks))    
    start<-as.data.frame(matrix(0,ncol = 3, nrow = 23))
    names(start)<-names(nfl_cur)
    
    for(i in 1:sims) {

    start[1,]<- nfl_cur %>% sample_n(1)
    nfl_cur2 <- subset(nfl_cur, !(wteam %in% start$wteam))
    nfl_cur2 <- subset(nfl_cur, !(week %in% start$week))

    start[2,]<-nfl_cur2 %>% sample_n(1)
    nfl_cur3 <- subset(nfl_cur2, !(wteam %in% start$wteam))
    nfl_cur3 <- subset(nfl_cur2, !(week %in% start$week))
    
    start[3,]<-nfl_cur3 %>% sample_n(1)
    nfl_cur4 <- subset(nfl_cur3, !(wteam %in% start$wteam))
    nfl_cur4 <- subset(nfl_cur3, !(week %in% start$week))
        ...
    outs[,i]<-start$dif  
    }

然后我重复直到我到达 23。但是，当我运行代码时，在第一次迭代之后，“out”数据帧被填充为 0，我假设因为 nfl_cur 仍在从开始过滤。

任何帮助将不胜感激！

Answer 1

如果我理解了，这可能会对你有所帮助

#Libraries

library(dplyr)

#Example Data
df <-
  structure(list(wteam = c("a", "a", "b", "c", "c", "d" ), week = c(1, 1, 1, 2, 2, 2), dif = c(0.649077088, 0.089812768,  0.173061282, 0.362544332, 0.459545808, 0.331745704)), row.names = c(NA,  6L), class = "data.frame")

#Sample 1 by each wteam + week

df %>% 
  group_by(wteam,week) %>% 
  sample_n(1)

# A tibble: 4 x 3
# Groups:   wteam, week [4]
  wteam  week    dif
  <chr> <dbl>  <dbl>
1 a         1 0.0898
2 b         1 0.173 
3 c         2 0.363 
4 d         2 0.332 

Answer 2

data.table 的选项

library(data.table)
setDT(df)[, .SD[sample(seq_len(.N), 1)], .(wteam, week)]

-输出

wteam week        dif
1:     a    1 0.08981277
2:     b    1 0.17306128
3:     c    2 0.36254433
4:     d    2 0.33174570