返回 r 中出现次数最多的字符值

Question

我有:

df<-data.frame(group=c(1, 1, 1, 1, 2, 2, 2), 
               char=c("a", "b", "z", "a", "c", "c", "b"),
               want=c("a", "a", "a", "a", "c", "c", "c"))
df

  group char want
1     1    a    a
2     1    b    a
3     1    z    a
4     1    a    a
5     2    c    c
6     2    c    c
7     2    b    c

我想按组返回 char 变量中出现次数最多的值。如果有解决关系的方法(即，如果第 1 组中有两个 a 和两个 b 这么说)，那也是理想的。

谢谢

Answer 1

我们可以使用 here 中的 Mode 函数要获得最频繁的值，按“组”进行分组，然后在“字符”列上应用该函数

library(dplyr)
Mode <- function(x) {
   ux <- unique(x)
   tabl <- tabulate(match(x, ux))
   i1 <- tabl == max(tabl)
   stopifnot(sum(i1) == 1)
   toString(ux[i1])
   }

df %>%
   group_by(group) %>%
   mutate(want = Mode(char))
# A tibble: 7 x 3
# Groups:   group [2]
#  group char  want 
#  <dbl> <fct> <fct>
#1     1 a     a    
#2     1 b     a    
#3     1 z     a    
#4     1 a     a    
#5     2 c     c    
#6     2 c     c    
#7     2 b     c    

用关系测试

df$char[2] <- 'z'

df %>%
   group_by(group) %>%
   mutate(want = Mode(char))

Error: `mutate()` argument `want` errored.
ℹ `want` is `Mode(char)`.
ℹ The error occured in group 1: group = 1.
✖ sum(i1) == 1 is not TRUE