expand_month.R

#' Expand month
#'
#' @param df dataframe to create monthly avg series
#'
#' @return a monthly average of the initial df
#' @export
expand_month <- function(df) {

  daily <- df %>%
    rowwise() %>%
    mutate(
      date_start = as.Date(date) - 6,
    ) %>%
    relocate(date_start, .after = date) %>%
    do(
      data.frame(.[1:2], daily = seq(.$date_start, .$date, by = "1 day"))
    ) %>%
    left_join(df, by = "date")

  avg <- daily %>%
    rowwise() %>%
    mutate(
      year = year(daily),
      month = month(daily),
      date_day = lubridate::days_in_month(as.Date(
        paste(year, month, "01", sep = "-"), "%Y-%m-%d")),
      date_monthly = as.Date(
        paste(year, month, date_day, sep = "-"), "%Y-%m-%d")
    ) %>%
    select(-c(date, date_start, date_day, year, month)) %>%
    group_by(date_monthly) %>%
    summarise(across(where(is.numeric), ~ mean(.x, na.rm = TRUE)))

  month <- avg %>%
    rename_all(list(~ (paste0(make.names(names(df)), "m")))) %>%
    rename("date" = "datem")

  return(month)

}