如何按组对变量求和 [英] How to sum a variable by group

问题描述

我有一个包含两列的数据框。第一列包含第一，第二，第三等类别，第二列具有代表我从类别中看到特定组的次数的数字。

I have a data frame with two columns. First column contains categories such as "First", "Second", "Third", and the second column has numbers that represent the number of times I saw the specific groups from "Category".

例如：

Category     Frequency
First        10
First        15
First        5
Second       2
Third        14
Third        20
Second       3

我想按类别对数据进行排序并汇总所有频率：

I want to sort the data by Category and sum all the Frequencies:

Category     Frequency
First        30
Second       5
Third        34

我将如何在R中做到这一点？

How would I do this in R?

推荐答案

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：

---

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) ...

---

（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)

---

或 tapply ：

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

---

使用此数据：

---

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))

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