date_range_merge.R

library(tidyverse)

library(lubridate) # for the days() function
library(fuzzyjoin) # for the fuzzy_left_join() function

climate <- read_tsv('./timetable.csv')
#  date         temperature
#1 2018-11-21   100 
#2 2018-11-22    80 

milk <- read_tsv('./milk.csv')

#  date         yield
#1 2018-11-22   150
# turn the characters of dates into proper Date objects
milk <- milk %>% mutate(date = as.Date(date, format = "%d/%m/%Y"))
climate <- climate %>% mutate(date = as.Date(date, format='%d/%m/%Y'))


# make a start and end range with plus/minus 7 days
climate$start <- climate$date - days(7)
climate$end <- climate$date + days(7)

# fuzzy left join on the range
fuzzy_left_join(
  milk, climate,
  by = c(
    # left table: by date
    # right table: by start and end
    "date" = "start",
    "date" = "end"
  ),
  # say that date of left table has to be bigger or equal to start of right table
  # say that date of left table has to be smalller or equal to end of right table
  match_fun = list(`>=`, `<=`)
)