如何按组获取平均值？ [英] How can I get mean values by group?

问题描述

我想按组高低分别获得var1和var2的平均值。
如何获得按组（低和高）分别表示的两个变量的平均值？

I want to get mean of var1 and var2 by group low and high. How can I get mean of two variables each by group (low and high) ?

 ID     var1       var2      low     high 
 1        1          6        0        1
 2        2          7        0        1
 3        3          8        1        0
 4        4          9        1        0
 5        5         10        0        1

推荐答案

聚合在给出正确输入的情况下满足您的需求。

aggregate does what you need, given the proper input.

要获取多个列的聚合，您可以可以 cbind 使其成为结果中的单独列：

To get the aggregate of multiple columns, you can cbind them so that they are separate columns in the result:

aggregate(cbind(var1, var2) ~ low+high, data=x, FUN=mean)
##   low high     var1     var2
## 1   1    0 3.500000 8.500000
## 2   0    1 2.666667 7.666667

如果要获取除以外的所有其他列的均值低和高，。很方便，意思是所有其他列：

If you want to take the mean of every column other than low and high, . is handy, meaning "all other columns":

aggregate(. ~ low+high, data=x, FUN=mean)
##   low high       ID     var1     var2
## 1   1    0 3.500000 3.500000 8.500000
## 2   0    1 2.666667 2.666667 7.666667

请注意， + 在公式中具有特殊含义如果它在〜的右侧。这并不意味着总和，而是意味着同时使用两个因素。在左侧，表示加法。

Note that + has a special meaning in the formula if it is on the right side of the ~. It doesn't mean a sum, but it means using both factors. On the left side, it means addition.

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