R function 返回“字符（0）”而不是基本方向

Question

I am attempting to convert wind direction (values 0-360) into a cardinal direction (ie NW). My code is below:

DegToDer <- function(degree) {
  value <- as.integer((degree / 45)+ .5)
  direction <- c("N","NE","E","SE","S","SW","W","NW")
  return(direction[((value+1) %% 8)])}

When I run it on my column I get the following error:

replacement has 346 rows, data has 365

I've tested it out with a few values and found out that every thing that should return the value "NE" is only returning "character (0)"

> DegToDer(293)
character(0)
> DegToDer(292)
[1] "W"
> DegToDer(360)
[1] "N"

Any and all assistance on this issue is greatly appreciated!

Answer 1

So, the problem here is that R indexes vectors starting at 1, so if you provide a value like floor((293/45)+0.5)+1 that returns 8, your index will be 0 and the function return value will be NA

How about you try to work with the base R function cut ?

DegToDer <- function (degree) {
  return(cut(
    x = degree,
    breaks = c(0, seq(22.5, 337.5, 45), 360),
    labels = c("N","NE","E","SE","S","SW","W","NW","N"),
    include.lowest = TRUE
  ))
}

Answer 2

You %% formula is slightly wrong.

degree <- 0:90

DegToDer <- function(degree) {
    value <- as.integer(degree / 45 + 0.5)
    direction <- c("N","NE","E","SE","S","SW","W","NW")
    return(direction[(value %% 8) + 1])
}

table(DegToDer(degree))
#> 
#>  E  N NE 
#> 23 23 45

^{Created on 2019-11-04 by the reprex package (v0.3.0)}