将满足所有可能标准的所有值相加

我有一个 data.table 如下所示：

a <- data.table(color=c("Red","Blue","Red","Green","Red","Blue","Blue"), count=c(1,2,6,4,2,1,1),include=c(1,1,1,1,0,0,1))

> a
     color count include
[1,]   Red     1       1
[2,]  Blue     2       1
[3,]   Red     6       1
[4,] Green     4       1
[5,]   Red     2       0
[6,]  Blue     1       0
[7,]  Blue     1       1

我希望创建一个新的 data.table，它仅具有唯一的颜色值，以及每个匹配 include=1 的计数列的总和，如下所示：

     colour total
[1,]   Red     7
[2,]  Blue     2
[3,] Green     4  

我尝试过以下方法，并且在过去取得了一些成功：

> a[,include == 1,list(total=sum(count)),by=colour]
Error in `[.data.table`(a, , include == 1, list(quantity = sum(count)),  : 
  Provide either 'by' or 'keyby' but not both

当以下情况时，也会收到同样的错误消息：a没有密钥，当它有密钥时colour。我也尝试过，将密钥设置为colour， 下列：

> a[,include == 1,list(quantity=sum(count))]
Error in `[.data.table`(a, , include == 1, list(quantity = sum(count))) : 
  Each item in the 'by' or 'keyby' list must be same length as rows in x (7): 1

我找不到其他好的解决方案。非常感谢任何帮助。

这应该有效

library(data.table)
a <- data.table(color=c("Red","Blue","Red","Green","Red","Blue","Blue"), count=c(1,2,6,4,2,1,1),include=c(1,1,1,1,0,0,1))
a[include == 1, list(total=sum(count)), keyby = color]

   color total
1:  Blue     3
2: Green     4
3:   Red     7

马修编辑：

Or if include（仅）取值0 and 1 then :

a[, list(total=sum(count*include)), keyby = color]

or if include包括其他值：

a[, list(total=sum(count*(include==1))), keyby = color]

where NA可能需要考虑。

通过避免矢量扫描，这些可能会更有效i，但这在很大程度上取决于数据大小和属性。这些只需要与最大组一样大的工作记忆，而include==1 in i需要至少分配一个向量，只要nrow(a).