#!/usr/bin/env python
# coding: utf-8

# # Parameter `arrow` for `geom_spoke()`
# 
# Note that the lengths of the arrow heads depend on the total lengths of the arrows.

# In[1]:


import numpy as np

from lets_plot import *


# In[2]:


LetsPlot.setup_html()


# In[3]:


def F(xarray, yarray):
    return yarray, -xarray

def cartesian_to_polar(xarray, yarray):
    rarray = np.sqrt(xarray**2 + yarray**2)
    return rarray / rarray.max(), np.arctan2(yarray, xarray)


# In[4]:


n = 11
a, b = -5, 5
space = np.linspace(a, b, n)
X, Y = np.meshgrid(space, space)
R, A = cartesian_to_polar(*F(X, Y))
data = dict(x=X.reshape(-1), y=Y.reshape(-1), r=R.reshape(-1), a=A.reshape(-1))


# In[5]:


ggplot(data, aes('x', 'y', color='r')) + \
    geom_spoke(aes(angle='a', radius='r'), \
               arrow=arrow(type='closed', angle=12, length=15)) + \
    scale_color_gradient(low='#3288bd', high='#d53e4f', guide='none') + \
    coord_fixed(xlim=[a, b], ylim=[a, b]) + \
    theme_minimal() + \
    theme(axis_text=element_text(margin=10), axis_title='blank')