Matplotlib - Recreating stackplot gridlines rendering in plot with fill_between - matplotlib

Question

I need to recreate a stackplot as a simple plot with fill_between (no stacking). The gridlines rendering appear to differ and I can't figure out how to make them look the same. Here's the code:
import pandas as pd
import numpy as np
mpl.rcParams.update(mpl.rcParamsDefault)
plt.style.use("ggplot")
_styles = {
'axes.edgecolor': '#bcbcbc',
'axes.facecolor': 'white',
'grid.color': '#b2b2b2',
'grid.linestyle': '--',
}
plt.rcParams.update(_styles)
def plot_a_plot(x_axis, actual, predicted, size=(10,4)):
plt.figure(figsize=size)
p1 = plt.plot(x_axis, actual, alpha=0.5, label=actual.name, lw=0.5)
plt.fill_between(x_axis, actual.astype(np.float64), color='#F0A498', alpha=1, zorder=1)
p2 = plt.plot(x_axis, predicted, alpha=0.5, label=predicted.name, lw=0.5)
plt.fill_between(x_axis, predicted.astype(np.float64), color='C1', alpha=0.5, zorder=0)
plt.grid(True, zorder=10)
plt.title('Plot with fill_between')
plt.show()
def plot_a_stackplot(x_axis, actual, predicted, size=(10,4)):
y = np.vstack([actual.astype(float), predicted.astype(float)])
plt.figure(figsize=size)
plt.stackplot(x_axis, y, labels=[actual.name, predicted.name], alpha=0.5, edgecolors="face")
plt.title('Stackplot')
plt.show()
arr = np.random.rand(10)
data = {
"actual": arr,
"predicted": arr*2
}
df = pd.DataFrame(data)
x_axis = df.index
actual = df['actual']
predicted = df['predicted']
plot_a_plot(x_axis, actual, predicted)
plot_a_stackplot(x_axis, actual, predicted)
View example here
Changing zorder doesn't seem to have any effect, I also played with alpha levels etc - nothing seems to work. The gridlines on stackplot just look the way it's meant to look, and gridlines on simple plot look muddy.

Answer 1

It seems that zorder doesn't work well with the value 0. In this demo, it is always chosen >=1.
The gird will look the same as with stackplot if you change your function to:
def plot_a_plot(x_axis, actual, predicted, size=(10,4)):
plt.figure(figsize=size)
p1 = plt.plot(x_axis, actual, alpha=0.5, label=actual.name, lw=0.5)
plt.fill_between(x_axis, actual.astype(np.float64), color='#F0A498', alpha=1, zorder=2)
p2 = plt.plot(x_axis, predicted, alpha=0.5, label=predicted.name, lw=0.5)
plt.fill_between(x_axis, predicted.astype(np.float64), color='C1', alpha=0.5, zorder=1)
plt.grid(True, zorder=10)
plt.title('Plot with fill_between')
plt.show()
Edit: if you want the bottom area (red) to look exactly like with stackplot, you should use the right color. You can find out colors with:
for color in plt.rcParams['axes.prop_cycle']:
print(color)
The first one is the one you're looking for: #E24A33 (C0 would work too)
From there, the second call on fill_between should fill between actual and predicted, otherwise the fill areas will overlap:
def plot_a_plot(x_axis, actual, predicted, size=(10,4)):
plt.figure(figsize=size)
p1 = plt.plot(x_axis, actual, alpha=0.5, label=actual.name, lw=0.5)
plt.fill_between(x_axis, actual.astype(np.float64), color='#E24A33', alpha=0.5, zorder=2)
p2 = plt.plot(x_axis, predicted, alpha=0.5, label=predicted.name, lw=0.5)
plt.fill_between(x_axis, actual, predicted, color='C1', alpha=0.5, zorder=1)
plt.grid(True, zorder=10)
plt.title('Plot with fill_between')
plt.show()

Answer 2

Try the following (I've not added the labels in this example):
def plot_a_plot(x_axis, actual, predicted, size=(10, 4)):
fig, ax = plt.subplots(figsize=size)
ax.plot(x_axis, actual, lw=0.5, alpha=0.5)
ax.fill_between(
x_axis,
actual,
np.zeros_like(data["actual"]), # explicitly set the "bottom" to be zero (this is the default so isn't actually required here)
color='#F0A498',
alpha=0.5, # set alpha to 0.5
zorder=1
)
ax.plot(x_axis, predicted, lw=0.5, alpha=0.5)
ax.fill_between(
x_axis,
predicted,
actual, # explicitly set the "bottom" to be actual, so it doesn't cover actual
color='C1',
alpha=0.5,
zorder=0
)
ax.grid(zorder=10)
fig.show()
This is essentially what is being done by stackplot (although it obviously plots the cumulative "top" and "bottom").