draw_vectors.R

draw_vector <- function(x, ...) {
  df <- data.frame(x1 = x[1], x2 = x[2])
  a <- arrow(length = unit(0.03, "npc"))
  dims <- ceiling(abs(max(x)))
  p <- ggplot() + xlim(-dims, dims) + ylim(-dims, dims)
  p <- p + geom_segment(aes(x = 0, y = 0, xend = x1, yend = x2), 
                        arrow = a, data = df, ...) +
    geom_hline(yintercept = 0, size = 0.1) +
    geom_vline(xintercept = 0, size = 0.1)
  return(p)
}

add_vector <- function(p, x, ...) {
  df <- data.frame(x1 = x[1], x2 = x[2])
  dims_x <- ceiling(abs(max(x)))
  dimx_p <- ceiling(abs(layer_scales(p)$x$range$range))
  dimy_p <- ceiling(abs(layer_scales(p)$y$range$range))
  dims <- max(c(dims_x, dimx_p, dimy_p))
  a <- arrow(length = unit(0.03, "npc"))
  p <- p + geom_segment(aes(x = 0, y = 0, xend = x1, yend = x2), 
                        arrow = a, data = df, ...) +
    xlim(-dims, dims) + ylim(-dims, dims)
  return(p)
}

# rotate a vector
rotate <- function(v, theta) {
  R <- matrix(c(cos(theta), sin(theta), 
               -sin(theta), cos(theta)), ncol = 2)
  return(R %*% v)
}