为什么group_by和mutate给我意外的结果？

Question

这是我的数据集的摘录：

check = structure(list(currency = c("AED", "ATS", "AUD", "BEF", "BND", 
"CAD"), year = c(2005, 2005, 2005, 2005, 2005, 2005), value = c(0, 
0, 14628, 0, 27, 1604), month = c("1", "1", "1", "1", "1", "1"
), quarter = c(1, 1, 1, 1, 1, 1)), row.names = c(NA, 6L), class = "data.frame")

运行此代码：

check2 = check %>% group_by(currency) %>% mutate(sum = sum(value))

给我

currency  year value  month   quarter   sum
  <chr>    <dbl> <dbl> <chr>   <dbl> <dbl>
1 AED       2005     0 1           1 16259
2 ATS       2005     0 1           1 16259
3 AUD       2005 14628 1           1 16259
4 BEF       2005     0 1           1 16259
5 BND       2005    27 1           1 16259
6 CAD       2005  1604 1           1 16259

每种货币都给我不同的价值吗？当我尝试按变量的不同组合进行分组时，它给我的值是16259。有人可以指出我在哪里做错了吗？谢谢。