Replace a value NA with the value from another column in R

问题

I want to replace the NA value in dfABy from the column A, with the value from the column B, based on the year of column year. For example, my df is:

                 >dfABy 
                 A    B   Year
                 56   75  1921
                 NA   45  1921
                 NA   77  1922
                 67   41  1923
                 NA   65  1923

The result what I will attend is:

                 > dfABy
                 A    B   Year
                 56   75  1921
                *45*  45  1921
                *77*  77  1922
                 67   41  1923
                *65*  65  1923

P.S: with the * the value replacing in column A from column B for every year

回答1:

Perhaps the easiest to read/understand answer in R lexicon is to use ifelse. So borrowing Richard's dataframe we could do:

df <- structure(list(A = c(56L, NA, NA, 67L, NA),
                     B = c(75L, 45L, 77L, 41L, 65L),
                     Year = c(1921L, 1921L, 1922L, 1923L, 1923L)),.Names = c("A", 
                                                                                                                            "B", "Year"), class = "data.frame", row.names = c(NA, -5L))
df$A <- ifelse(is.na(df$A), df$B, df$A)

回答2:

You could use simple replacement with [<-, subsetting for the NA elements.

df$A[is.na(df$A)] <- df$B[is.na(df$A)]

Or alternatively, within()

within(df, A[is.na(A)] <- B[is.na(A)])

Both give

   A  B Year
1 56 75 1921
2 45 45 1921
3 77 77 1922
4 67 41 1923
5 65 65 1923

Data:

df <- structure(list(A = c(56L, NA, NA, 67L, NA), B = c(75L, 45L, 77L, 
41L, 65L), Year = c(1921L, 1921L, 1922L, 1923L, 1923L)), .Names = c("A", 
"B", "Year"), class = "data.frame", row.names = c(NA, -5L))

回答3:

Easy

library(dplyr)

dfABy %>%
  mutate(A_new = 
           A %>% 
             is.na %>%
             ifelse(B, A) )

回答4:

The new dplyr function, coalesce, can really simplify these situations.

library(dplyr)

dfABy %>% 
    coalesce(A,B)

回答5:

The solution provided by GGAnderson did return an error message. Using it inside mutate() however worked fine.

df <- structure(list(A = c(56L, NA, NA, 67L, NA),
                     B = c(75L, 45L, 77L, 41L, 65L),
                     Year = c(1921L, 1921L, 1922L, 1923L, 1923L)),
                .Names = c("A", "B", "Year"), 
                class = "data.frame", 
                row.names = c(NA, -5L))
df
df%>% 
  coalesce(A,B) #returns error

df %>%
mutate(A = coalesce(A,B)) #works

(I am new to Stackoverflow; My low reputation does not allow to comment on GGAnderson´s answer directly)

来源：https://stackoverflow.com/questions/34071875/replace-a-value-na-with-the-value-from-another-column-in-r

标签

replace