Plot horizontal and vertical joining lines for coordinates described by arrays `x` & `y`.

plot_lines.py

# coding: utf-8
"""
Plot horizontal and vertical joining lines for coordinates described by
arrays `x` & `y`.
"""
import numpy as np
import matplotlib.pyplot as plt

def lines(x, y, first='x', ax=None, **kwargs):
    """
    Args:
        `x` & `y`: coordinates suitable for passing to a scatter plot.
        `first`: `'x'` or `'y'`. Draw lines along this axis first.
        `ax`: axis on which to plot lines.
    """
    try:
        assert first in ('x', 'y')
    except:
        raise
    else:
        if first == 'x':
            ax.hlines(y[:-1], x[:-1], x[1:], **kwargs)
            ax.vlines(x[1: ], y[:-1], y[1:], **kwargs)
        else:
            ax.hlines(y[1: ], x[:-1], x[1:], **kwargs)
            ax.vlines(x[:-1], y[:-1], y[1:], **kwargs)
        return ax

if __name__ == "__main__":
    x = np.random.rand(10).cumsum()
    y = np.random.rand(10)
    fig, ax = plt.subplots()
    ax.scatter(x, y)
    lines(x, y, first='x', ax=ax, linestyles='dashed', colors='r', alpha=0.5)
    lines(x, y, first='y', ax=ax, linestyles='dotted', colors='b', alpha=0.5)
    fig.show()