r - 与 dplyr 等长的组

Question

我有 df:

df <- data.frame(group = c(rep("G1",18), rep("G2", 10)), X = c(rep("a", 10), rep("b", 8), rep("c", 4), rep("d", 6)), Y = c(rep(1:10), rep(1:8), rep(1:4), rep(1:6)))

可能通过使用 dplyr 或 tidyr，我想让每个 group 中的所有子组具有相同的长度，应该是组元素中最小的一个。 简而言之，生成的数据框应该是:

df_r <- data.frame(group = c(rep("G1",16), rep("G2", 8)), X = c(rep("a", 8), rep("b", 8), rep("c", 4), rep("d", 4)), Y = c(rep(1:8), rep(1:8), rep(1:4), rep(1:4)))

我无法专注于如何实现这一目标。任何帮助将不胜感激。

Answer 1

这可能是您想要的？

library(dplyr)
df_r <- df %>% group_by(group, X) %>% mutate(maxY = max(Y)) %>% 
               group_by(group) %>% filter(Y <= min(maxY)) %>% select(group, X, Y)

> df_r
   group X Y
1     G1 a 1
2     G1 a 2
3     G1 a 3
4     G1 a 4
5     G1 a 5
6     G1 a 6
7     G1 a 7
8     G1 a 8
9     G1 b 1
10    G1 b 2
11    G1 b 3
12    G1 b 4
13    G1 b 5
14    G1 b 6
15    G1 b 7
16    G1 b 8
17    G2 c 1
18    G2 c 2
19    G2 c 3
20    G2 c 4
21    G2 d 1
22    G2 d 2
23    G2 d 3
24    G2 d 4

> df_r1 <- data.frame(group = c(rep("G1",16), rep("G2", 8)), X = c(rep("a", 8), rep("b", 8), rep("c", 4), rep("d", 4)), Y = c(rep(1:8), rep(1:8), rep(1:4), rep(1:4)))
> identical(df_r, df_r1)
[1] TRUE