Matplotlib_Create_Waterfall_chart.md

Template request | Bug report | Generate Data Product

Tags: #matplotlib #chart #warterfall #dataviz #snippet #operations #image

Author: Jeremy Ravenel

Description: This notebook provides instructions on how to create a Waterfall chart using Matplotlib.

Input

Import library

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
from matplotlib.ticker import FuncFormatter

Model

Create the waterfall chart

# Use python 2.7+ syntax to format currency
def money(x, pos):
    "The two args are the value and tick position"
    return "${:,.0f}".format(x)


formatter = FuncFormatter(money)

# Data to plot. Do not include a total, it will be calculated
index = ["sales", "returns", "credit fees", "rebates", "late charges", "shipping"]
data = {"amount": [350000, -30000, -7500, -25000, 95000, -7000]}

# Store data and create a blank series to use for the waterfall
trans = pd.DataFrame(data=data, index=index)
blank = trans.amount.cumsum().shift(1).fillna(0)

# Get the net total number for the final element in the waterfall
total = trans.sum().amount
trans.loc["net"] = total
blank.loc["net"] = total

# The steps graphically show the levels as well as used for label placement
step = blank.reset_index(drop=True).repeat(3).shift(-1)
step[1::3] = np.nan

# When plotting the last element, we want to show the full bar,
# Set the blank to 0
blank.loc["net"] = 0

# Plot and label
my_plot = trans.plot(
    kind="bar",
    stacked=True,
    bottom=blank,
    legend=None,
    figsize=(10, 5),
    title="2014 Sales Waterfall",
)
my_plot.plot(step.index, step.values, "k")
my_plot.set_xlabel("Transaction Types")

# Format the axis for dollars
my_plot.yaxis.set_major_formatter(formatter)

# Get the y-axis position for the labels
y_height = trans.amount.cumsum().shift(1).fillna(0)

# Get an offset so labels don't sit right on top of the bar
max = trans.max()
neg_offset = max / 25
pos_offset = max / 50
plot_offset = int(max / 15)

# Start label loop
loop = 0
for index, row in trans.iterrows():
    # For the last item in the list, we don't want to double count
    if row["amount"] == total:
        y = y_height[loop]
    else:
        y = y_height[loop] + row["amount"]
    # Determine if we want a neg or pos offset
    if row["amount"] > 0:
        y += pos_offset
    else:
        y -= neg_offset
    my_plot.annotate("{:,.0f}".format(row["amount"]), (loop, y), ha="center")
    loop += 1

Output

Display result

# Scale up the y axis so there is room for the labels
my_plot.set_ylim(0, blank.max() + int(plot_offset))
# Rotate the labels
my_plot.set_xticklabels(trans.index, rotation=0)
my_plot.get_figure().savefig("waterfall.png", dpi=200, bbox_inches="tight")