R-按组汇总并具有某些功能 [英] R - aggregate by group with some function

问题描述

我想按特定组和操作汇总数据框

I want to aggregate a data frame by a certain group and operation

数据

> df <- data.frame(replicate(9, 1:4))
  X1 X2 X3 X4 X5 X6 X7 X8 X9
1  1  1  1  1  1  1  1  1  1
2  2  2  2  2  2  2  2  2  2
3  3  3  3  3  3  3  3  3  3
4  4  4  4  4  4  4  4  4  4

聚合

> aggregate(df[,2], list(df[,1]), mean)
  Group.1 x
1       1 1
2       2 2
3       3 3
4       4 4

上述汇总非常有用。但是，代替平均值，我需要使用平均值* sd / length ^ 2 之类的功能组合。我们是否应该在这里使用除聚合以外的其他方法？

The above aggregation works, which is great. However instead of mean, in place of that I need to use combination of functions like mean*sd/length^2. Should we be using something other than aggregate here ?

推荐答案

我修改了示例数据框，以便获取每个组的长度和标准差（您不能这样做

I modified your sample data frame in order to get a length and standard deviation for each group (you can't do this with only one data point per group).

> df
   X1 X2 X3 X4 X5 X6 X7 X8 X9
1   1  1  1  1  1  1  1  1  1
2   2  2  2  2  2  2  2  2  2
3   3  3  3  3  3  3  3  3  3
4   4  4  4  4  4  4  4  4  4
5   1  1  1  1  1  1  1  1  1
6   2  2  2  2  2  2  2  2  2
7   3  3  3  3  3  3  3  3  3
8   4  4  4  4  4  4  4  4  4
9   1  4  4  4  4  4  4  4  4
10  2  5  5  5  5  5  5  5  5
11  3  6  6  6  6  6  6  6  6
12  4  7  7  7  7  7  7  7  7
13  1  4  4  4  4  4  4  4  4
14  2  5  5  5  5  5  5  5  5
15  3  6  6  6  6  6  6  6  6
16  4  7  7  7  7  7  7  7  7

要通过更详细的公式进行汇总，请执行以下操作：

To aggregate by a more elaborated formula do:

aggregate(df[,2], list(df[,1]), function(x){mean(x)*sd(x)/length(x)^2})
  Group.1         x
1       1 0.2706329
2       2 0.3788861
3       3 0.4871393
4       4 0.5953925

如果要具有相同的列标签，可以执行以下操作：

If you want to have the same column labels you could do:

aggregate(list(X2 = df[,2]), list(X1 = df[,1]), function(x){mean(x)*sd(x)/length(x)^2})
  X1        X2
1  1 0.2706329
2  2 0.3788861
3  3 0.4871393
4  4 0.5953925

（或随后使用姓氏重命名）

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