ggplot堆叠的barplot：更改颜色时出现问题

Question

我的数据框如下：

test <- structure(list(score = c(5L, 4L, 3L, 2L, 1L, 5L, 4L, 3L, 2L, 
1L), plate = c("A", "A", "A", "A", "A", "B", "B", "B", "B", "B"
), n = c(84.6153846153846, 15.3846153846154, NA, NA, NA, 19.2307692307692, 
30.7692307692308, 34.6153846153846, 15.3846153846154, NA)), .Names = c("score", 
"plate", "n"), row.names = c(NA, 10L), class = "data.frame")

我正在使用以下方法创建堆叠的条形图：

ggplot (data = test, aes (x = plate, y = n, fill = score)) +
  geom_bar (stat = 'identity')

我想定义自己的填充色。我正在尝试这样做（例如）：

ggplot (data = test, aes (x = plate, y = n, fill = score)) +
  geom_bar (stat = 'identity') + 
  scale_fill_brewer (palette = 'Dark2')

它说：

  

错误：连续值提供给离散刻度

与我使用scale_fill_manual() ...

你能帮忙吗？