Question

我想在一个列中但在分组列定义的组中重新排列因子的水平。

简单的示例数据集：

df <- structure(list(a_factor = structure(1:6, .Label = c("a", "b", 
"c", "d", "e", "f"), class = "factor"), group = structure(c(1L, 
1L, 1L, 2L, 2L, 2L), .Label = c("group1", "group2"), class = "factor"), 
value = 1:6), class = "data.frame", row.names = c(NA, -6L
))

> df
  a_factor  group value
1        a group1     1
2        b group1     2
3        c group1     3
4        d group2     4
5        e group2     5
6        f group2     6

更准确地说，如何重新排序因子水平，例如在value处下降df$group == "group1"，在value处上升df$group == "group2"，最好在dplyr中上升？

预期输出可能是：

> df
  a_factor  group value
1        c group1     3
2        b group1     2
3        a group1     1
4        d group2     4
5        e group2     5
6        f group2     6

尽管如此，问题更普遍的是如何在dplyr中解决此问题。

Answer 1

我们可以根据组值取反，然后订购：

df %>% 
  arrange(case_when(
    group == "group1" ~ -value,
    group == "group2" ~ value))

#   a_factor  group value
# 1        c group1     3
# 2        b group1     2
# 3        a group1     1
# 4        d group2     4
# 5        e group2     5
# 6        f group2     6

Answer 2

以下是基本的R解决方案。

sp <- split(df$value, df$group)
sp <- lapply(seq_along(sp), function(i) sort(sp[[i]], decreasing = i == 1))
df$a_factor <- factor(df$a_factor, levels = df$a_factor[unlist(sp)])

df$a_factor
#[1] a b c d e f
#Levels: c b a d e f

df[order(df$a_factor), ]
#  a_factor  group value
#3        c group1     3
#2        b group1     2
#1        a group1     1
#4        d group2     4
#5        e group2     5
#6        f group2     6

Answer 3

一种选择是执行group_split并传递list对应于arrange需要如何执行的逻辑值

library(tidyverse)   
df %>% 
    group_split(group) %>%
    map2_df(., list(FALSE, TRUE), ~ if(.y) .x %>%
       arrange(value) else  .x %>% arrange(desc(value)))
# A tibble: 6 x 3
#  a_factor group  value
#  <fct>    <fct>  <int>
#1 c        group1     3
#2 b        group1     2
#3 a        group1     1
#4 d        group2     4
#5 e        group2     5
#6 f        group2     6

Answer 4

要重新排序因子水平，可以使用forcats（tidyverse的一部分），并执行类似的操作...

library(forcats)
df2 <- df %>% mutate(a_factor = fct_reorder(a_factor,
                                            value*(-1 + 2 * (group=="group1"))))

levels(df2$a_factor)
[1] "f" "e" "d" "a" "b" "c"

这不会重新排列数据框本身...

df2
  a_factor  group value
1        a group1     1
2        b group1     2
3        c group1     3
4        d group2     4
5        e group2     5
6        f group2     6

组内的重新排序因子级别

4 个答案: