R 如何基于初始列a、B、C值设置列C值

我有下表：

A     B       C
food  fruit   apple
food  fruit   
food  drink
food  fruit   
car   suv     ford
car   sedan   bmw
car   suv
car   sedan

预期结果：

 A     B       C
food  fruit   apple
food  fruit   apple
food  drink
food  fruit   apple 
car   suv     ford
car   sedan   bmw
car   suv     ford
car   sedan   bmw

如何根据A列和B列中的值填写C列？例如，如果A列中的值=食物，B列中的值=水果，则C列中应填入。理想情况下，我希望这样做而不必手动输入A、B列对和相应的C列值，因为我的表有数千个这样的组合

---

非常感谢您的帮助

这里是一个使用data.table的解决方案

library(data.table)
setDT(dx)[,id:=1:.N] ## create variable to conserve origin order

dx[,C:={
  val <- unique(C[nzchar(C)])  
  if(length(val)==0) val <- ""    ## case empty C
  if(length(val)>1) val <- val[1] ## case multiple values

  rep(val,length(C))
  }, "A,B"][order(id)][,id:=NULL]

#       A     B     C
# 1: food fruit apple
# 2: food fruit apple
# 3: food drink      
# 4: food fruit apple
# 5:  car   suv  ford
# 6:  car sedan   bmw
# 7:  car   suv  ford
# 8:  car sedan   bmw

库（data.table）
setDT（dx）[，id:=1.N]##创建变量以保留原始顺序
dx[，C:={
val使用
数据的两个备选方案。表
：

library(data.table)
setDT(d1)[, C := C[C != ''], by = .(A,B)][]
setDT(d1)[, C := ifelse(all(C == ''), '', C[C != '']), by = .(A,B)][]

两者都给出：


使用
dplyr
的替代方法：

library(dplyr)
d1 %>% 
  group_by(A, B) %>% 
  summarise(C = ifelse(all(C == ''), '', C[C != ''])) %>% 
  right_join(., d1, by = c('A','B')) %>% 
  select(A, B, C = C.x)

library(dplyr)
library(tidyr)

df %>%
  mutate(C = ifelse(C == "", NA, C)) %>%
  group_by(A, B) %>%
  fill(C) 

这给出了类似的结果。
从
tidyr
中填充
的溶液：

library(dplyr)
d1 %>% 
  group_by(A, B) %>% 
  summarise(C = ifelse(all(C == ''), '', C[C != ''])) %>% 
  right_join(., d1, by = c('A','B')) %>% 
  select(A, B, C = C.x)

library(dplyr)
library(tidyr)

df %>%
  mutate(C = ifelse(C == "", NA, C)) %>%
  group_by(A, B) %>%
  fill(C) 

结果：

# A tibble: 8 x 3
# Groups:   A, B [4]
      A     B     C
  <chr> <chr> <chr>
1   car sedan   bmw
2   car sedan   bmw
3   car   suv  ford
4   car   suv  ford
5  food drink  <NA>
6  food fruit apple
7  food fruit apple
8  food fruit apple

# A tibble: 8 x 3
# Groups:   A, B [4]
      A     B     C
  <chr> <chr> <chr>
1  food fruit apple
2  food fruit apple
3  food drink  <NA>
4  food fruit apple
5   car   suv  ford
6   car sedan   bmw
7   car   suv  ford
8   car sedan   bmw

df = structure(list(A = c("food", "food", "food", "food", "car", "car", 
"car", "car"), B = c("fruit", "fruit", "drink", "fruit", "suv", 
"sedan", "suv", "sedan"), C = c("apple", "", "", "", "ford", 
"bmw", "", "")), .Names = c("A", "B", "C"), class = "data.frame", row.names = c(NA, 
-8L))

结果：

# A tibble: 8 x 3
# Groups:   A, B [4]
      A     B     C
  <chr> <chr> <chr>
1   car sedan   bmw
2   car sedan   bmw
3   car   suv  ford
4   car   suv  ford
5  food drink  <NA>
6  food fruit apple
7  food fruit apple
8  food fruit apple

# A tibble: 8 x 3
# Groups:   A, B [4]
      A     B     C
  <chr> <chr> <chr>
1  food fruit apple
2  food fruit apple
3  food drink  <NA>
4  food fruit apple
5   car   suv  ford
6   car sedan   bmw
7   car   suv  ford
8   car sedan   bmw

df = structure(list(A = c("food", "food", "food", "food", "car", "car", 
"car", "car"), B = c("fruit", "fruit", "drink", "fruit", "suv", 
"sedan", "suv", "sedan"), C = c("apple", "", "", "", "ford", 
"bmw", "", "")), .Names = c("A", "B", "C"), class = "data.frame", row.names = c(NA, 
-8L))

我已经成功地使用了你的建议：setDT（d1）[，C:=C[C！=”]，by=（A，B）][]我想知道如果我有一个额外的列需要填充，我如何应用这个，列D。例如，一行有以下值：A=食物B=水果C=苹果D=红色。如果另一行有A=食物，B=水果，C=（空白），D=（空白），我想用C=apple，D=red来填充那一行中的列。非常感谢您的帮助。谢谢！有什么建议吗？@user6340762抱歉，由于除夕庆祝活动忘了回到这一行；一个可能的解决方案：
setDT（d1）[，`:=`（C=C[C！=''，D=D[D！=''），by=（a，B）]
一点问题都没有，当然可以理解！这似乎很有效。谢谢！有没有关于如何/如果我可以忽略某些例外情况的建议？例如，大多数行的值是a=食物B=水果C=苹果D=红色。但有几行的值是a=食物B=水果C=香蕉D=黄色。在填充其他内容时，如何可以忽略这些例外情况空白行，如果A=食物，B=水果，所有空白的C，D列总是用C=苹果和D=红色（不是C=香蕉，D=黄色）填充。谢谢！