通过ID用非NA值替换NA

Question

在df中，我想用每个ID的非NA值替换NA值

id<-c(1,1,1,1,2,2,2)
price<-c(NA,20,NA,NA,NA,NA,5)
df<-data.frame(id,price)

 id    price
  1       NA
  1       20
  1       NA
  1       NA
  2       NA
  2       NA
  2        5

理想情况下，输出应如下所示：

id      price
  1       20
  1       20
  1       20
  1       20
  2        5
  2        5
  2        5

任何帮助将不胜感激。

Answer 1

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data.table