Conditional recoding of factor to factor

I have a tibble, df, with a factor, A, I wish to:

1) copy of,C, and
2) recode based on a second variable, B.

At the moment I'm doing it in this roundabout way. I'm quite confused by the conditional recoding of factor. I also looked at dplyr's recode, but couldn't work out a smarter method.

library(tibble)
df  <- tibble(
  A = factor(c(NA, "b", "c")), 
  B = c(1,NA,3)
)

My initial tibble

df
#> # A tibble: 3 x 2
#>        A     B
#>   <fctr> <dbl>
#> 1   <NA>     1
#> 2      b    NA
#> 3      c     3

Step #1 in my current solution

df$C <- with(df, ifelse(is.na(B), 'B is NA', A)) 
df
#> # A tibble: 3 x 3
#>        A     B       C
#>   <fctr> <dbl>   <chr>
#> 1   <NA>     1    <NA>
#> 2      b    NA B is NA
#> 3      c     3       2

Step #2 in my current solution

df$C <- dplyr::recode_factor(df$C, '2' = 'c')
df
#> # A tibble: 3 x 3
#>        A     B       C
#>   <fctr> <dbl>  <fctr>
#> 1   <NA>     1    <NA>
#> 2      b    NA B is NA
#> 3      c     3       c

How am I suppose to do this?

Solution

Using dplyr::if_else, convert factor to character, then convert to factor again:

library(dplyr)

df %>% 
  mutate(C = factor(if_else(is.na(B), "B is NA", as.character(A))))

# # A tibble: 3 x 3
#          A     B       C
#     <fctr> <dbl>  <fctr>
#   1   <NA>     1    <NA>
#   2      b    NA B is NA
#   3      c     3       c