合并R中数据框的列

Question

I have the following data frame,

c1 <- c(1,2,"<NA>","<NA>")
c2 <- c("<NA>","<NA>",3,4)
df <- data.frame(c1,c2)

>df 

    c1   c2
1    1 <NA>
2    2 <NA>
3 <NA>    3
4 <NA>    4

The following is the desired output that I'm trying to obtain after merging columns 1 ,2

  >df 

    c1  
1    1 
2    2
3    3
4    4

I tried,

df <- mutate(df, x =paste(c1,c2))

which gives

> df
    c1   c2      x
1    1 <NA> 1 <NA>
2    2 <NA> 2 <NA>
3 <NA>    3 <NA> 3
4 <NA>    4 <NA> 4

Could someone give suggestions on how to obtain the desired output?

Answer 1

One way is this:

c1 <- c(1, 2, NA, NA)
c2 <- c(NA, NA, 3, 4)
df <- data.frame(c1, c2)

df2 <- data.frame(
  c1 = ifelse(is.na(df$c1), df$c2, df$c1)
)

#df2
#  c1
#1  1
#2  2
#3  3
#4  4

Answer 2

You are close, but you are pasting together two strings where one uses the string NA in angled brackets to represent nothing, and if you are pasting strings together and want a string to not appear in the pasted string you need to have it as a zero length string. You can do this using the recode command in dplyr .

You can modify your code to be:

library(dplyr)
df <- mutate(df, x =paste0(recode(c1,"<NA>" = ""),recode(c2,"<NA>" = "")))

Answer 3

Another way using dplyr from tidyverse :

df2 <- df %>% 
    mutate(c3 = if_else(is.na(c1),c2,c1)) %>% 
    select(-c1, -c2) %>% # Given you only wanted one column
    rename(c1 = c3) # Given you wanted the column to be called c1

Output:

  c1
1  1
2  2
3  3
4  4

Answer 4

You could use rowSums :

data.frame(c1 = rowSums(df,na.rm = TRUE))
#   c1
# 1  1
# 2  2
# 3  3
# 4  4

Answer 5

Since it seems the the dataframe actually contains NA values rather than '<NA>' strings, I would suggest to use coalesce :

c1 <- c(1,2,NA, NA)
c2 <- c(NA, NA,3,4)
df <- data.frame(c1,c2)

library(tidyverse)
df %>% 
  mutate(c3=coalesce(c1, c2))

Output:

   c1 c2 c3
1  1 NA  1
2  2 NA  2
3 NA  3  3
4 NA  4  4