Scatter Plot

A small example for creating scatter plot with Magick back-end.

require 'rmagick'
$canvas_height = 100
$canvas_width = 100
$horizontal_border = 10
$vertical_border = 10
$canvas = Magick::ImageList.new
$canvas.new_image($canvas_height+2*$vertical_border, $canvas_width+2*$horizontal_border, Magick::HatchFill.new('white', 'gray90'))

def draw_axes
  axes = Magick::Draw.new
  axes.polyline($horizontal_border,$canvas_height+$vertical_border, $canvas_width+$horizontal_border,$canvas_height+$vertical_border,
    $horizontal_border,$canvas_height+$vertical_border, $horizontal_border,$vertical_border)
  axes.draw($canvas)
end

def transform_x(x, max_x)
  ($canvas_width * x ) / max_x + $horizontal_border 
end

def transform_y(y, max_y)
  ($canvas_height * (max_y - y)) / max_y + $vertical_border
end

def write(filename)
  $canvas.write(filename)
end

def display
  $canvas.display
end

def scatter(x,y,marker_size)
  max_x = x.max
  max_y = y.max
  x.each_with_index do |ix, idx_x|
    iy = y[idx_x]
    ix = transform_x(ix,max_x)
    iy = transform_y(iy,max_y)
    marker = Magick::Draw.new
    marker.circle(ix,iy, ix+marker_size,iy)
    marker.draw($canvas)
  end
end

def run()
  x = [10,12,74,65]
  y = [150,100,57,46]
  draw_axes
  scatter(x,y,2)
  write("example.png")
end

run()

Saving the figure for the scatter plot for the points (10,150),(12,100),(74,57) and (65,46) gives the output: