聚合/总结每组的多个变量(例如总和、平均值) [英] Aggregate / summarize multiple variables per group (e.g. sum, mean)

问题描述

从一个数据框中，是否有一种简单的方法可以同时聚合(sum、mean、max 等)多个变量?

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

以下是一些示例数据:

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)

我想按年和月同时聚合 df2 数据框中的 x1 和 x2 变量.下面的代码聚合了x1变量，但是否也可以同时聚合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)

推荐答案

这个 year() 函数来自哪里?

Where is this year() function from?

你也可以使用 reshape2 包来完成这个任务:

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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