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# The Helper Functions Called by the Main Function
#' Helper function to reorder the values in the input flight dataframe.
#'
#'@param df A two-column dataframe - The start and end airports of flights.
#'
#'@return A two-column dataframe
#'
#' @examples
#' arrange_path(sample_trips)
#'
#' @export
arrange_path <- function(df) {
for (i in seq_along(1:nrow(df))) {
if (df[i,1] > df[i,2]) {
tmp <- df[i,1]
df[i,1] <- df[i,2]
df[i,2] <- tmp
}
}
return(df)
}
#' Helper function to calculate the coordinate limits of map border
#'
#' Since the world map is huge, and flights are usually drawn in a relatively\cr
#' small area, the map needs to be cropped based on the coordinates of airports\cr
#' used. This function generates the coordinate limits of the cropped map.
#'
#'@param v A double numeric vector - vector of longtitudes/latitudes.
#'@param type A string - "long" or "lat". It indicates whether longtitudes or latitudes are input.
#'@param padding_ratio A double number - 0 to 1. The padding ratio is defined as\cr
#'padding / (maximum - minimum)
#'
#'@return A two-column dataframe
#'
#' @examples
#' get_map_border(c(-20,30,60,85), type = "lat")
#' get_map_border(c(-10,0,10,40), type = "long", padding_ratio = 0.2)
#'
#' @export
get_map_border <- function(v,
type = c("long", "lat"),
padding_ratio = 0.1) {
padding <- (max(v) - min(v)) * padding_ratio
extreme <- ifelse(type == "long", 180, 90)
return(c(max(min(v) - padding, -extreme),
min(max(v) + padding, extreme)))
}
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