Summing rows by month in R

Question

So I have a data frame that has a date column, an hour column and a series of other numerical columns. Each row in the data frame is 1 hour of 1 day for an entire year.

Answer 1

This could be another way to do this using data.table

library(data.table)
# Edited as per Arun's comment
out = setDT(data)[, lapply(.SD, sum), by=Date] 

#>out
#         Date Hour Melbourne Southern Flagstaff
#1: 2009-05-01   21         0      496       715

or by using dplyr

library(dplyr)
out = data %>% group_by(Date) %>% summarise_each(funs(sum))

#>out
#Source: local data frame [1 x 5]
#        Date Hour Melbourne Southern Flagstaff
#1 2009-05-01   21         0      496       715