Reorder position of NA's when using group_by

Question

I would like to reorder the position of NA's in a column, within each level of another categorical variable. For example with this data frame:

df <- data.frame(fact=c(1,1,1,2,2,2), id=rep(1:6), value=c(NA,44,23,NA,NA,76))

I would like to mutate a new column like:

df$newvar <= c(44,23,NA,76,NA,NA)

I would have thought the following would work, but it doesn't:

dfb <- df %>% group_by(fact) %>% mutate(newvar = df$value[order(is.na(df$value))])

Any ideas on how I can do this?

Answer 1

You should remove the df$ part in your mutate statement, otherwise you are referring to the full column, instead of the column per group. So this should work fine:

df %>% group_by(fact) %>% mutate(newvar = value[order(is.na(value))])

Output:

# A tibble: 6 x 4
# Groups: fact [2]
   fact    id value newvar
  <dbl> <int> <dbl>  <dbl>
1  1.00     1  NA     44.0
2  1.00     2  44.0   23.0
3  1.00     3  23.0   NA  
4  2.00     4  NA     76.0
5  2.00     5  NA     NA  
6  2.00     6  76.0   NA