Euler 19

How many sundays fell on the first of the month in the period 1 january 1901 to 31 december 2000?

library(tidyverse)

Construct vector with all dates from january first 1901 to december 31st 2000.

Filter to only get the first of every month. And to get sundays (running this on a danish computer, so “søndag”).

Get number of rows:

answer <- as_date(as_date("1901-01-01"):as_date("2000-12-31")) %>% 
  as_tibble() %>% 
  filter(day(value) == 1,
         weekdays(value) == "søndag") %>% 
  nrow()