r - Calculating change of values between same day in different years -

i need calculate called mat (movie anual total), means % change in sales value between same day in 2 different year:

    id sales day month year      500   31  12   2015      100   1    1   2016      200   2    1   2016      ...            200   1    1   2017 

does have idea how deal it?

i want this:

id sales day month yeas **mat** 

with way data set up, you're quite close. want group data month , day, order each group year, , take successive differences (assuming want mat sequential years)

library(lubridate) library(dplyr) x <-    data.frame(date = seq(as.date("2014-01-01"),                          as.date("2017-12-31"),                          = 1)) %>%   mutate(day = day(date),          month = month(date),          year = year(date),          sales = rnorm(nrow(.), mean = 100, sd = 5))  x %>%   group_by(month, day) %>%   arrange(month, day, year) %>%   mutate(mat = c(na, diff(sales))) %>%   ungroup() 

if wanting able generically take difference between 2 years, need refinements.