使用聚合：

aggregate(x$Frequency, by=list(Category=x$Category), FUN=sum)
  Category  x
1    First 30
2   Second  5
3    Third 34

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在上面的示例中，多次暗淡可以在列表中指定。可以通过 cbind 合并同一数据类型的多个聚合指标：

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In the example above, multiple dimensions can be specified in the list. Multiple aggregated metrics of the same data type can be incorporated via cbind:

aggregate(cbind(x$Frequency, x$Metric2, x$Metric3) ...

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（嵌入@thelatemail评论），汇总也具有公式界面

aggregate(Frequency ~ Category, x, sum)

或如果要聚合多个列，则可以使用。表示法（也适用于一列）

Or if you want to aggregate multiple columns, you could use the . notation (works for one column too)

aggregate(. ~ Category, x, sum)

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或 tapply ：

tapply(x$Frequency, x$Category, FUN=sum)
 First Second  Third 
    30      5     34 

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使用此数据：

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Using this data:

x <- data.frame(Category=factor(c("First", "First", "First", "Second",
                                      "Third", "Third", "Second")), 
                    Frequency=c(10,15,5,2,14,20,3))