use ifelse to create new column in r

问题

My code is:

data$E<-ifelse(data$D==data$B, "b", ifelse(data$D==data$C, "c", "unknowwn"))

result:

  A   B   C   D   E
1 16  16  NA  16  b
2 20  NA  20  20  NA
3 24  NA  NA  24  NA

But what I want is:

  A   B   C   D   E
1 16  16  NA  16  b
2 20  NA  20  20  c
3 24  NA  NA  24  unknowwn

Dose anyone know how to solve this problem? Thanks!

回答1:

data$E <- ifelse(!is.na(data$B) & data$D == data$B, "b", 
            ifelse(!is.na(data$C) & data$D == data$C, "c", "unknowwn"))

回答2:

Your condition is a bit complicated as you need to consider if either of columns B, C or D contains NA. Hence, you can try consider using dplyr::case_when as:

Edited: Based on suggestion from @A.Suliman there is no need to have checking for is.na with case_when.

library(dplyr)

data %>% mutate( E = case_when(
  D==B ~ "b",
  D==C ~ "c",
  TRUE ~ "Unknown"
))

#    A  B  C  D       E
# 1 16 16 NA 16       b
# 2 20 NA 20 20       c
# 3 24 NA NA 24 Unknown

Data:

data <- read.table(text= 
"A   B   C   D   
1 16  16  NA  16  
2 20  NA  20  20
3 24  NA  NA  24",
header = TRUE)

来源：https://stackoverflow.com/questions/51348877/use-ifelse-to-create-new-column-in-r