Reversing legend and data order for geom_bar

I have a dataframe (df) as follows

I have been able to create a bar graph with this

ggplot(df, aes(x=result, y=count, fill = id)) +
  geom_bar(stat = "identity") +
  labs(x = "Example", y = "Frequency", fill = "Group") + 
  scale_x_discrete(labels = c("Positive", "Negative"))

The resulting bar graph looks like this

However, I want the Positive to be on the left and i want group a to be blue. How would the modified code look like if i had multiple results (e.g., positive, negative, unknown, small)?

Character variables mapped to aesthetics (such as x, y, fill, color, etc) in ggplot are converted into factors, and are arranged in the order of the factor levels. Unless you pass a factor with the desired ordering of levels to the discrete scale, they will therefore be arranged alphabetically, since this is the default behaviour when factors are created.

So we simply do this to get the desired ordering:

ggplot(df, aes(factor(result, c('positive', 'negative')), count, 
               fill = factor(id, c('b', 'a')))) +
  geom_col() +
  labs(x = "Example", y = "Frequency", fill = "Group") + 
  scale_x_discrete(labels = c("Positive", "Negative")) +
  scale_fill_discrete(breaks = c('a', 'b'))