MikeTP - 6 months ago 40

R Question

From a data frame, is there a easy way to aggregate (i.e. sum) multiple variables simultaneously?

Below are some sample data:

`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)

I would like to simultaneously aggregate the

`x1`

`x2`

`df2`

`x1`

`x2`

`### aggregate variables by year month`

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

head(df2)

Any suggestions would be greatly appreciated.

Answer

Where is this year() function from?

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
```