Função para escrever número da semana entrando com data formato YYYY-mm-dd (conferir em http://whatweekisit.org/calendar-2018.html)

write_week.R

date_ini = '2018-05-10'
get_week_numbers = function(date_ini){
	# Week number of first day from next month (1st week)
	week_ini = as.integer(format(as.Date(date_ini), '%W'))
	# Week number of first day from next-next month (4th or 5th week) minus 1 (+2 pra completar 6 semanas)
	date_end_temp = as.character(as.Date(date_ini) + 31)
	date_end = paste(strsplit(date_end_temp, '-')[[1]][1], strsplit(date_end_temp, '-')[[1]][2], '01', sep = '-')
	week_end = as.integer(format(as.Date(date_end), '%W')) - 1 + 2
	# Return array with year and week numbers
	year = format(as.Date(date_ini), '%Y')
	c(as.numeric(year), as.numeric(week_ini), as.numeric(week_end))
}