每组汇总/汇总多个变量（例如，总和，均值）

问题描述

从数据框架中，有一种简单的方法来汇总（总和，平均值， max 等c）同时使用多个变量吗？

From a data frame, is there a easy way to aggregate (sum, mean, max et c) multiple variables simultaneously?

下面是一些示例数据：

library(lubridate)
days = 365*2
date = seq(as.Date("2000-01-01"), length = days, by = "day")
year = year(date)
month = month(date)
x1 = cumsum(rnorm(days, 0.05)) 
x2 = cumsum(rnorm(days, 0.05))
df1 = data.frame(date, year, month, x1, x2)

我想同时汇总中的 x1 和 x2 变量df2 数据框按年份和月份显示。以下代码汇总了 x1 变量，但是是否也可以同时汇总 x2 变量？

I would like to simultaneously aggregate the x1 and x2 variables from the df2 data frame by year and month. The following code aggregates the x1 variable, but is it also possible to simultaneously aggregate the x2 variable?

### aggregate variables by year month
df2=aggregate(x1 ~ year+month, data=df1, sum, na.rm=TRUE)
head(df2)

任何建议将不胜感激。

推荐答案

此 year（）函数从哪里来？

您也可以使用 reshape2 软件包完成此任务：

You could also use the reshape2 package for this task:

require(reshape2)
df_melt <- melt(df1, id = c("date", "year", "month"))
dcast(df_melt, year + month ~ variable, sum)
#  year month         x1           x2
1  2000     1  -80.83405 -224.9540159
2  2000     2 -223.76331 -288.2418017
3  2000     3 -188.83930 -481.5601913
4  2000     4 -197.47797 -473.7137420
5  2000     5 -259.07928 -372.4563522

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