循环遍历r中的组

Question

我有一个df，包括一组数据帧，df1,df2和df3，其中每个数据帧遵循以下结构:

df1 <- data.frame(year = c("2013", "2013", "2013", "2013", "2013","2013"), 
site = c("a", "a", "a", "a", "a", "a"),
trt = c("x", "y", "x", "y", "x", "y"),
cover = c(2, 5, 1,20,50,12))
df2 <- data.frame(year = c("2014", "2014", "2014", "2014", "2014","2014"),
site = c("a", "a", "a", "a", "a", "a"),
trt = c("x", "y", "x", "y", "x", "y"),
cover = c(1, 3, 1,24,32,12))
df3 <- data.frame(year = c("2015", "2015", "2015", "2015", "2015","2015"),
site = c("a", "a", "a", "a", "a", "a"),
trt = c("x", "y", "z", "z", "x", "y"),
cover = c(2, 5, 1,2,11,32))
df <- rbind(df1, df2, df3)
df
year site trt cover
1  2013    a   x     2
2  2013    a   y     5
3  2013    a   x     1
4  2013    a   y    20
5  2013    a   x    50
6  2013    a   y    12
7  2014    a   x     1
8  2014    a   y     3
9  2014    a   x     1
10 2014    a   y    24
11 2014    a   x    32
12 2014    a   y    12
13 2015    a   x     2
14 2015    a   y     5
15 2015    a   z     1
16 2015    a   z     2
17 2015    a   x    11
18 2015    a   y    32

我过去使用for loop对每年cover列中的值进行排序。

v1 <- unique(df$year)
lst <- list()
for (i in seq_along(v1)) {
lst[[i]] <- df |> 
filter(year == v1[i]) |> 
mutate(rank = dense_rank(desc(cover)))
}

现在，我正试图对每年每个组(如trt列中定义的)的值进行排名，但我不知道如何做到这一点。我怎么能做到这一点与for loop。我愿意得到lapply函数的答案，因为我想了解它。

Answer 1

使用dplyr，我们可以通过在mutate之前使用group来避免循环和过滤，然后使用group_split来构建列表。

library(dplyr)
df |>
group_by(year) |>
mutate(rank = dense_rank(desc(cover))) |>
group_split()

输出:

[[1]]
# A tibble: 6 × 5
year  site  trt   cover  rank
<chr> <chr> <chr> <dbl> <int>
1 2013  a     x         2     5
2 2013  a     y         5     4
3 2013  a     x         1     6
4 2013  a     y        20     2
5 2013  a     x        50     1
6 2013  a     y        12     3
[[2]]
# A tibble: 6 × 5
year  site  trt   cover  rank
<chr> <chr> <chr> <dbl> <int>
1 2014  a     x         1     5
2 2014  a     y         3     4
3 2014  a     x         1     5
4 2014  a     y        24     2
5 2014  a     x        32     1
6 2014  a     y        12     3
[[3]]
# A tibble: 6 × 5
year  site  trt   cover  rank
<chr> <chr> <chr> <dbl> <int>
1 2015  a     x         2     4
2 2015  a     y         5     3
3 2015  a     z         1     5
4 2015  a     z         2     4
5 2015  a     x        11     2
6 2015  a     y        32     1