colorline.py

# Topics: line, color, LineCollection, cmap, colorline, codex
'''
Defines a function colorline that draws a (multi-)colored 2D line with coordinates x and y.
The color is taken from optional data in z, and creates a LineCollection.

z can be:
- empty, in which case a default coloring will be used based on the position along the input arrays
- a single number, for a uniform color [this can also be accomplished with the usual plt.plot]
- an array of the length of at least the same length as x, to color according to this data
- an array of a smaller length, in which case the colors are repeated along the curve

The function colorline returns the LineCollection created, which can be modified afterwards.

See also: plt.streamplot
'''

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.collections import LineCollection
from matplotlib.colors import ListedColormap, BoundaryNorm


# Data manipulation:

def make_segments(x, y):
    '''
    Create list of line segments from x and y coordinates, in the correct format for LineCollection:
    an array of the form   numlines x (points per line) x 2 (x and y) array
    '''

    points = np.array([x, y]).T.reshape(-1, 1, 2)
    segments = np.concatenate([points[:-1], points[1:]], axis=1)
    
    return segments


# Interface to LineCollection:

def colorline(x, y, z=None, cmap=plt.get_cmap('copper'), norm=plt.Normalize(0.0, 1.0), linewidth=3, alpha=1.0):
    '''
    Plot a colored line with coordinates x and y
    Optionally specify colors in the array z
    Optionally specify a colormap, a norm function and a line width
    '''
    
    # Default colors equally spaced on [0,1]:
    if z is None:
        z = np.linspace(0.0, 1.0, len(x))
           
    # Special case if a single number:
    if not hasattr(z, "__iter__"):  # to check for numerical input -- this is a hack
        z = np.array([z])
        
    z = np.asarray(z)
    
    segments = make_segments(x, y)
    lc = LineCollection(segments, array=z, cmap=cmap, norm=norm, linewidth=linewidth, alpha=alpha)
    
    ax = plt.gca()
    ax.add_collection(lc)
    
    return lc
        
    
def clear_frame(ax=None): 
    # Taken from a post by Tony S Yu
    if ax is None: 
        ax = plt.gca() 
    ax.xaxis.set_visible(False) 
    ax.yaxis.set_visible(False) 
    for spine in ax.spines.itervalues(): 
        spine.set_visible(False)