python + matplotlib: how to insert more space between the axis and the tick labels in a polar chart?

charts, matplotlib, python

Solution

@dabillox already mentioned using the `frac` kwarg to `ax.set_thetagrids`.

However, as you've noticed, what you're really wanting to change is the alignment of the ticklabels, rather than the overall radial displacement of the tick labels.

On a side note, the reason that `labelpad` had no effect is that it controls the padding between the axis label (e.g. `plt.xlabel`, `plt.ylabel`) and the axis, not the tick labels.

First off, you could write your example code a bit more cleanly. Here's more-or-less how I would approach what you're doing (note that this will still have the same problem with tick label positioning):

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.ticker as tkr

def main():
    data = [ 10.49531611,  22.49511583,  10.90891806,  18.99525417,
            21.57165972,   6.687755  ,   6.52137028,  15.86534639,
            18.53823556,   6.32563583,  12.99365833,  11.06817056,
            17.29261306,  15.31288556,  19.16236667,  10.38483333,
            14.51442222,  17.01413611,   6.96102278,  15.98508611,
            16.5287    ,  15.26533889,  20.83520278,  17.21952056,
             7.3225775 ,  16.42534361,  14.38649722,  21.63573111,  16.19249444]
    data = np.array(data)*60*60
    plot_clock(data)
    plt.show()

def plot_clock(data):
    def hour_formatAM(x, p):
        hour = x * 6 / np.pi
        return '{:0.0f}:00'.format(hour) if x > 0 else '12:00'

    def hour_formatPM(x, p):
        hour = x * 6 / np.pi
        return '{:0.0f}:00'.format(hour + 12) if x > 0 else '24:00'

    def plot(ax, theta, counts, formatter):
        colors = plt.cm.jet(theta / 12.0)
        ax.bar(theta, counts, width=np.pi/6, color=colors, alpha=0.5)
        ax.xaxis.set_major_formatter(tkr.FuncFormatter(formatter))

    plt.rcParams['font.size'] = 8

    bins = np.r_[0, 0.5:12, 12, 12.5:24,  23.99999]
    data = np.array(data) / (60*60)
    counts = np.histogram(data,bins)[0]

    counts[13] += counts[0]
    counts[-1] += counts[13]

    fig, axes = plt.subplots(ncols=2, figsize=(5.5, 3), dpi=200,
                             subplot_kw=dict(projection='polar'))
    fig.subplots_adjust(wspace=0.4)
    for ax in axes:
        ax.set(theta_offset=np.pi/2, theta_direction=-1,
               xticks=np.arange(0, np.pi*2, np.pi/6),
               yticks=np.arange(1, counts.max()))

    plot(axes[0], bins[1:13] * np.pi / 6, counts[1:13], hour_formatAM)
    plot(axes[1], bins[14:26] * np.pi / 6, counts[14:26], hour_formatPM)

main()

If we want to avoid the mis-aligned tick labels, we can set the horizontal alignment based on their position:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.ticker as tkr

def main():
    data = [ 10.49531611,  22.49511583,  10.90891806,  18.99525417,
            21.57165972,   6.687755  ,   6.52137028,  15.86534639,
            18.53823556,   6.32563583,  12.99365833,  11.06817056,
            17.29261306,  15.31288556,  19.16236667,  10.38483333,
            14.51442222,  17.01413611,   6.96102278,  15.98508611,
            16.5287    ,  15.26533889,  20.83520278,  17.21952056,
             7.3225775 ,  16.42534361,  14.38649722,  21.63573111,  16.19249444]
    data = np.array(data)*60*60
    axes = plot_clock(data)
    for ax in axes:
        realign_polar_xticks(ax)
    plt.show()

def realign_polar_xticks(ax):
    for x, label in zip(ax.get_xticks(), ax.get_xticklabels()):
        if np.sin(x) > 0.1:
            label.set_horizontalalignment('left')
        if np.sin(x) < -0.1:
            label.set_horizontalalignment('right')

def plot_clock(data):
    def hour_formatAM(x, p):
        hour = x * 6 / np.pi
        return '{:0.0f}:00'.format(hour) if x > 0 else '12:00'

    def hour_formatPM(x, p):
        hour = x * 6 / np.pi
        return '{:0.0f}:00'.format(hour + 12) if x > 0 else '24:00'

    def plot(ax, theta, counts, formatter):
        colors = plt.cm.jet(theta / 12.0)
        ax.bar(theta, counts, width=np.pi/6, color=colors, alpha=0.5)
        ax.xaxis.set_major_formatter(tkr.FuncFormatter(formatter))

    plt.rcParams['font.size'] = 8

    bins = np.r_[0, 0.5:12, 12, 12.5:24,  23.99999]
    data = np.array(data) / (60*60)
    counts = np.histogram(data,bins)[0]

    counts[13] += counts[0]
    counts[-1] += counts[13]

    fig, axes = plt.subplots(ncols=2, figsize=(5.5, 3), dpi=200,
                             subplot_kw=dict(projection='polar'))
    fig.subplots_adjust(wspace=0.5)

    for ax in axes:
        ax.set(theta_offset=np.pi/2, theta_direction=-1,
               xticks=np.arange(0, np.pi*2, np.pi/6),
               yticks=np.arange(1, counts.max()))

    plot(axes[0], bins[1:13] * np.pi / 6, counts[1:13], hour_formatAM)
    plot(axes[1], bins[14:26] * np.pi / 6, counts[14:26], hour_formatPM)
    return axes

main()

And finally, if you want to do this "properly", regardless of the theta direction and offset, do something like:

def realign_polar_xticks(ax):
    for theta, label in zip(ax.get_xticks(), ax.get_xticklabels()):
        theta = theta * ax.get_theta_direction() + ax.get_theta_offset()
        theta = np.pi/2 - theta
        y, x = np.cos(theta), np.sin(theta)
        if x >= 0.1:
            label.set_horizontalalignment('left')
        if x <= -0.1:
            label.set_horizontalalignment('right')
        if y >= 0.5:
            label.set_verticalalignment('bottom')
        if y <= -0.5:
            label.set_verticalalignment('top')

Problem

Original source

Related problems

• matplotlib: adding padding/offset to polar plots tick labels