#' Calculate number of days since start of epidemics
#'
#' @param date_0 a Date
#' @return the number of days
#' between date in date_0
#' and start of the corresponding epidemic season
#' (1st Feb if date is in Feb-Jul,
#' 1st Aug if date is in Aug-Jan)
#' @export
date2nbDaysSinceEpid <- function(date_0){
spring <- (lubridate::month(date_0) %in% 2:7)
year <- lubridate::year(date_0)
if(spring){
return(as.numeric(date_0 -
as.Date(paste0('02/01/',as.numeric(year)),
format='%m/%d/%Y')))
}else{
res <- as.numeric(date_0 -
as.Date(paste0('08/01/',as.numeric(year)),
format='%m/%d/%Y'))
if(res < 0){
# if the peak is in january,
# the start of the season is in the previous year
res <- as.numeric(date_0 -
as.Date(paste0('08/01/',as.numeric(year)-1),
format='%m/%d/%Y'))
}
return(res)
}
}
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