playing around with recycling in R

recycling.R

recycle <- function(x, y, each = FALSE) {
  vals <- list(x, y)
  n <- lengths(vals)
  
  if (n[1] == n[2]) {
    return(vals)
  }
  
  
  if (n[1] == 0 | n[2] == 0) {
    return(vals)
  }
  
  if (n[1] == 1) {
    if (each) {
      vals[[1]] <- rep(vals[[1]],  each = n[2])
    } else {
      vals[[1]] <- rep(vals[[1]], times = n[2])
    }
    
    return(vals)
  }
  
  if (n[2] == 1) {
    if (each) {
      vals[[2]] <- rep(vals[[2]],  each = n[2])
    } else {
      vals[[2]] <- rep(vals[[2]], times = n[2])
    }
    
    return(vals)
  }
    
  if (n[1] < n[2]) {
    op <- 1
    min <- n[1]
    max <- n[2]
  } else {
    op <- 2
    min <- n[2]
    max <- n[1]
  }
  
  if (max %% min != 0) {
    stop("cannot recycle x and y")
  }
  
  if (each) {
    vals[[op]] <- rep(vals[[op]],  each = max %/% min)
  } else {
    vals[[op]] <- rep(vals[[op]], times = max %/% min)
  }
  
  vals
}

recycle(1:3, NULL)
recycle(c("this", "that"), 1:4)
recycle(c("this", "that"), 1:4, each = TRUE)