r - 基于相邻列最大值的值

Question

使用 group_by() 我想根据列 value2 的最大值获取列 value 的值:

df = data.frame(id = c(1,1,1,1,2,2,2,2),
                value = c(4,5,1,3,1,2,3,1),
                value2 = c("a","b","c","d","e","f","g","h"))

df %>% group_by(id) %>%
   sumarise(value2_of_largest_value = f(value, value2))

1  b
2  g

Answer 1

我们可以使用 which.max 获取 value 的索引，并使用它来对 value2 进行子集化

library(dplyr)
f1 <- function(x, y) y[which.max(x)]
df %>%
   group_by(id) %>%
   summarise(value2 = f1(value, value2))
   #or simply
   # summarise(value2 = value2[which.max(value)]) 
# A tibble: 2 x 2
#     id value2
#  <dbl> <fct> 
#1     1 b     
#2     2 g