Plotting different colors on bar chart values If the number falls below 0

Question

I need some help plotting my data. Is there a way to plot a bar graph with different colors. For example I would like to have a legend showing a green dot with the text positive and red dot with the text negative. Furthermore, if the graph value falls below 0 add a red color. If it is above 0 add a green color? Is this possible? Any help in the right direction would be greatly appreciated.

For example:

Is it possible?

See my code below:

    import matplotlib.pyplot as plt
    import pandas as pd
    import matplotlib
    import matplotlib.pyplot as plt


    fig, ax = plt.subplots()
    df = pd.DataFrame({'Years': ['2015', '2016', '2017', '2018'],
        'Value': [-495982.0, 405549.0, -351541.0, 283790.0]})
    values = df["Value"]
    values = values / 1e3
    asOfDates = df['Years']

    Value = df['Value']/100

    fig, ax = plt.subplots()
    ax.set_title('Plotting Financials')
    ax.set_xlabel('Years')
    ax.set_ylabel('value')
    plt.bar(asOfDates,values)
    ax.get_yaxis().set_major_formatter(matplotlib.ticker.FuncFormatter(lambda x, p: format(int(x), ',')))

    plt.show()

Answer 1

plt.bar accepts a parameter color= which either can be a single color, or a list with one color for each of the bars. The list can be constructed via list comprehension, giving a color depending on a constraint.

A bar plot normally only generates one entry in the legend (via plt.bar(..., label='my barplot'). To get more than one label, and also to have it circular instead of rectangular, custom legend elements can be created.

Here is some example code to get you started:

import pandas as pd
import matplotlib.pyplot as plt
from matplotlib.lines import Line2D
import matplotlib

df = pd.DataFrame({'Years': ['2015', '2016', '2017', '2018'],
                   'Value': [-495982.0, 405549.0, -351541.0, 283790.0]})
values = df["Value"]
values = values / 1e3
asOfDates = df['Years']

Value = df['Value'] / 100

fig, ax = plt.subplots()
ax.set_title('Plotting Financials')
ax.set_xlabel('Years')
ax.set_ylabel('value')
plt.bar(asOfDates, values, color=['r' if v < 0 else 'g' for v in values])
ax.get_yaxis().set_major_formatter(matplotlib.ticker.FuncFormatter(lambda x, p: format(int(x), ',')))

legend_handles = [Line2D([0], [0], linewidth=0, marker='o', markerfacecolor=color, markersize=12, markeredgecolor='none')
                  for color in ['g', 'r']]
ax.legend(legend_handles, ['positive', 'negative'])

plt.show()