Intuitive vector subsetting using keywords

keyword-vector-subsetting.R

`[.hmmm` <- function (x, i, ...) {
  
  isub <- substitute(i)
  
  is_seq <- identical(as.list(isub)[[1L]], as.name(":"))
  
  if (is_seq) {
    
    end_seq <- as.list(isub)[[3L]]
    is_end <- identical(end_seq, as.name("end"))
    
    if (is_end) {
      
      
      start <- as.integer(as.list(isub)[[2L]])
      end <- length(x)
      
      x <- unclass(x)[start:end]
      class(x) <- "hmmm"
      x
      
    } else {
      
      x <- unclass(x)[eval(isub)]
      class(x) <- "hmmm"
      x
      
    }
  } else {
    
    x <- unclass(x)[eval(isub)]
    class(x) <- "hmmm"
    x
    
  }
}

x <- 1:100
class(x) <- "hmmm"
x[99:end]
#> [1]  99 100
#> attr(,"class")
#> [1] "hmmm"