NCL_box_3.py

This script illustrates the following concepts:

• Drawing box plots

• Adding markers to a box plot

• Setting the color of individual boxes in a box plot

• Setting the width of individual boxes in a box plot

See following URLs to see the reproduced NCL plot & script:

• Original NCL script: https://www.ncl.ucar.edu/Applications/Scripts/box_3.ncl

• Original NCL plot: https://www.ncl.ucar.edu/Applications/Images/box_3_lg.png

Import packages:

import numpy as np
import matplotlib.pyplot as plt

import geocat.viz as gv

Generate fake data

np.random.seed(200)
data = np.random.lognormal(size=(40, 3), mean=1, sigma=0.7)
for a in range(len(data)):
    data[a] = [x - 4 for x in data[a]]

Helper function to set edge color of boxes

def setBoxColor(boxplot, colors):
    # Set edge color of the outside and median lines of the boxes
    for element in ['boxes', 'medians']:
        for box, color in zip(boxplot[element], colors):
            plt.setp(box, color=color)

    # Set the color of the whiskers and caps of the boxes
    for element in ['whiskers', 'caps']:
        for box, color in zip(
            zip(boxplot[element][::2], boxplot[element][1::2]), colors
        ):
            plt.setp(box, color=color)

Helper function to remove axis “spines” on the top and right sides

def removeSpines(ax):
    ax.spines['right'].set_visible(False)
    ax.spines['top'].set_visible(False)

Plot:

# Create figure and axis
fig, ax = plt.subplots(figsize=(6, 6))

# Plot each boxplot, set tick labels, and determine box widths
boxplots = ax.boxplot(
    data,
    tick_labels=['Control', '-2Xna', '2Xna'],
    widths=[0.4, 0.4, 0.4],
    showfliers=False,
)

# Set whisker style to dashed
plt.setp(boxplots['whiskers'], linestyle='--')

# Set boxplot edge colors
setBoxColor(boxplots, ['blue', 'red', 'green'])

# Use geocat.viz.util convenience function to set axes tick values
gv.set_axes_limits_and_ticks(ax, ylim=(-6.0, 9.0), yticks=[-3.0, 0.0, 3.0, 6.0])

# Use geocat.viz.util convenience function to add minor and major tick lines
gv.add_major_minor_ticks(ax, y_minor_per_major=3, x_minor_per_major=1, labelsize=14)

# Use geocat.viz.util convenience function to add title to the plot axis.
gv.set_titles_and_labels(ax, maintitle='Box Plot with Polymarkers')

# Make both major and minor ticks point inwards towards the plot
ax.tick_params(direction="in", which='both')

# Get rid of right and top axis spines
removeSpines(ax)

# Set ticks only at left and bottom sides of plot
ax.yaxis.set_ticks_position('left')
ax.xaxis.set_ticks_position('bottom')

# Add another partially transparent axis on top of the first one
ax2 = ax.inset_axes([0, 0, 1, 1])
ax2.patch.set_alpha(0.2)

# Set limits of second axis so markers will line up with boxes on boxplot
ax2.set_xlim(0, 6)
ax2.set_ylim(-6, 9)

# Turn both major and minor ticks in overlaid axis off
ax2.tick_params(
    which='both',
    top=False,
    bottom=False,
    left=False,
    right=False,
    labelleft=False,
    labelbottom=False,
)

# Get rid of right and top axis spines
removeSpines(ax2)

# Plot red x markers
ax2.scatter(1, 7.7, marker='x', color='red', linewidth=0.5, s=100)
ax2.scatter(3, 2.5, marker='x', color='red', linewidth=0.5, s=100)
ax2.scatter(5, 2, marker='x', color='red', linewidth=0.5, s=100)

# Plot blue o markers
ax2.scatter(1, 2, marker='o', color='darkblue')
ax2.scatter(3, -0.5, marker='o', color='darkblue')
ax2.scatter(5, 1, marker='o', color='darkblue')

plt.show()