r - Aggregate / summarize multiple variables per group (i.e. sum, mean, etc) -

from data frame, there easy way aggregate (i.e. sum) multiple variables simultaneously?

below sample data:

library(lubridate) days = 365*2 date = seq(as.date("2000-01-01"), length = days, = "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) 

i simultaneously aggregate x1 , x2 variables df2 data frame year , month. following code aggregates x1 variable, possible simultaneously aggregate x2 variable?

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

any suggestions appreciated.

where year() function from?

you use reshape2 package 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