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Help regarding matplotlib multicolored lines - attached StackOverflow question

Deep Sinha
Hi,

I needed some help tweaking a multicolored line with matplotlib. I adopted tacaswell's answer on StackOverflow at http://stackoverflow.com/a/30125761/3566440

When I do the steps exactly like its explained in the answer, I am able to replicate it. However, my case is a bit different. I have a dataframe with timeseries as it's index, and 'perc99_99' as a set of Z-scores. 

Inline image 1

I modified the SO answer to the best of my knowledge and this is what the code looks like:
fig, ax = plt.subplots()

# Index of dataframe = timestamps
x = day_avg_zscore.index.values
# Z score of 99th percentiles
y = day_avg_zscore['perc99_99'].values
# Threshold at Z-score = 2, using helper function
lc = threshold_plot(ax, x, y, 2, 'k', 'r')
ax.axhline(2, color='k', ls='--')
lc.set_linewidth(3)

plt.show()
I left the helper function intact:

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.collections import LineCollection
from matplotlib.colors import ListedColormap, BoundaryNorm

def threshold_plot(ax, x, y, threshv, color, overcolor):
"""
Helper function to plot points above a threshold in a different color

Parameters
----------
ax : Axes
Axes to plot to
x, y : array
The x and y values

threshv : float
Plot using overcolor above this value

color : color
The color to use for the lower values

overcolor: color
The color to use for values over threshv

"""
# Create a colormap for red, green and blue and a norm to color
# f' < -0.5 red, f' > 0.5 blue, and the rest green
cmap = ListedColormap([color, overcolor])
norm = BoundaryNorm([np.min(y), threshv, np.max(y)], cmap.N)

# Create a set of line segments so that we can color them individually
# This creates the points as a N x 1 x 2 array so that we can stack points
# together easily to get the segments. The segments array for line collection
# needs to be numlines x points per line x 2 (x and y)
points = np.array([x, y]).T.reshape(-1, 1, 2)
segments = np.concatenate([points[:-1], points[1:]], axis=1)

# Create the line collection object, setting the colormapping parameters.
# Have to set the actual values used for colormapping separately.
lc = LineCollection(segments, cmap=cmap, norm=norm)
lc.set_array(y)

ax.add_collection(lc)
ax.set_xlim(np.min(x), np.max(x))
ax.set_ylim(np.min(y)*1.1, np.max(y)*1.1)
return lc


Here's what I get as an output:

Inline image 2

What am I missing?

I'm using Anaconda Python2.7 and Jupyter Notebook.

Thank you!

- Deep
--
Sent from my phone. Please forgive typos and other forms of brevity.

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