r - 比较一列中的两行 R

Question

我想比较 R 中两行中一列中列出的值。这些行通过 ID 变量进行标识。我想生成一个新变量，告诉我两个值中哪个值低于另一个值。这是一个例子:

value   id   new_var
    1    1     lower
    2    1    higher
    5    2    higher
    3    2     lower
   10    3     lower
   11    3    higher
    2    4     lower
    1    4    higher

谢谢!

Answer 1

如果每组有两个以上元素，请进行分组，并使用 ifelse/case_when 创建条件来创建“new_var”

library(dplyr)
df1 %>% 
  group_by(id) %>% 
  mutate(new_var = case_when(value == max(value) ~ "higher",
      TRUE ~ "lower")) %>% 
  ungroup
# A tibble: 8 × 3
  value    id new_var
  <int> <int> <chr>  
1     1     1 lower  
2     2     1 higher 
3     5     2 higher 
4     3     2 lower  
5    10     3 lower  
6    11     3 higher 
7     2     4 higher 
8     1     4 lower  

---

还有一种选择是排列，然后按照rep的顺序创建一个新列(假设每个id有2个元素)

df1 %>%
  arrange(id, value) %>% 
  mutate(new_var = rep(c("lower", "higher"), length.out = n()))

数据

df1 <- structure(list(value = c(1L, 2L, 5L, 3L, 10L, 11L, 2L, 1L), id = c(1L, 
1L, 2L, 2L, 3L, 3L, 4L, 4L)), row.names = c(NA, -8L), class = "data.frame")