matplotlib advanced bar plot

Question

I need to recreate a chart similar to the one below created in Excel. I was hoping to use matplotlib, but can't seem to find any examples or reference for how to do a chart like this. I need to have bars colored based on a performance threshold, and also display the threshold. Can anyone point me in the right direction? I do need to be able to do this with Python, though.

Answer 1

I gotta run, but here's something to get you started:

import numpy as np
import matplotlib
matplotlib.rcParams['text.usetex'] = False
import matplotlib.pyplot as plt
import pandas

df = pandas.DataFrame(np.random.uniform(size=37)*100, columns=['A'])
threshold = 75
fig, ax = plt.subplots(figsize=(8,3))

good = df['A'][df['A'] >= threshold]
bad = df['A'][df['A'] < threshold]

ax.bar(left=good.index, height=good, align='center', color='ForestGreen', zorder=5)
ax.bar(left=bad.index, height=bad, align='center', color='Firebrick', zorder=5)

ax.axhline(y=threshold, linewidth=2, color='ForestGreen', zorder=0)

ax.set_xticks(df.index)
ax.set_xlim(left=df.index[0]-0.75, right=df.index[-1]+0.75)

def annotateBars(row, ax=ax):
    if row['A'] < 20:
        color = 'black'
        vertalign = 'bottom'
        vertpad = 2
    else:
        color = 'white'
        vertalign = 'top'
        vertpad = -2

    ax.text(row.name, row['A'] + vertpad, "{:.1f}%".format(row['A']),
            zorder=10, rotation=90, color=color,
            horizontalalignment='center',
            verticalalignment=vertalign,
            fontsize=8, weight='heavy')

junk = df.apply(annotateBars, ax=ax, axis=1)

And that gives me:

Answer 2

This can now be plotted much more concisely:

1. Axes.bar_label automatically labels bars (requires matplotlib 3.4.0+)
2. Axes.bar has a color param that can accept an array of colors (e.g. via numpy.where)

So now it only takes a handful of lines, e.g. using Paul's sample df = pd.DataFrame({'A': np.random.uniform(size=35) * 100}):

fig, ax = plt.subplots(figsize=(9, 3))
threshold = 75

# plot bars as blue if A > threshold, else red
color = np.where(df.A > threshold, 'blue', 'red')
ax.bar(x=df.index, height=df.A, color=color)

# add bar labels
ax.bar_label(ax.containers[0], fmt='%.1f%%')

# add threshold line
ax.axhline(threshold, alpha=0.5, zorder=0)

Or for multiple thresholds, just update color as desired (e.g. via numpy.select):

upper, lower = 75, 25
color = np.select([df.A > upper, df.A < lower], ['blue', 'red'], default='gray')

Note that a color array can also be passed into other bar plot helpers:

• DataFrame.plot.bar:

  df.plot.bar(y='A', color=color, ax=ax)
  

• Series.plot.bar:

  df.A.plot.bar(color=color, ax=ax)
  

• seaborn.barplot (as palette):

  sns.barplot(x=df.index, y=df.A, palette=color, ax=ax)