Running median of y-values over a range of x
matplotlib, median, numpy, python, scatter
Solution
I would use `np.digitize` to do the bin sorting for you. This way you can easily apply any function and set the range you are interested in.
import numpy as np
import pylab as plt
N = 2000
total_bins = 10
# Sample data
X = np.random.random(size=N)*10
Y = X**2 + np.random.random(size=N)*X*10
bins = np.linspace(X.min(),X.max(), total_bins)
delta = bins[1]-bins[0]
idx = np.digitize(X,bins)
running_median = [np.median(Y[idx==k]) for k in range(total_bins)]
plt.scatter(X,Y,color='k',alpha=.2,s=2)
plt.plot(bins-delta/2,running_median,'r--',lw=4,alpha=.8)
plt.axis('tight')
plt.show()
As an example of the versatility of the method, let's add errorbars given by the standard deviation of each bin:
running_std = [Y[idx==k].std() for k in range(total_bins)]
plt.errorbar(bins-delta/2,running_median,
running_std,fmt=None)
Problem
Below is a scatter plot I constructed from two numpy arrays. Scatter Plot Example What I'd like to add to this plot is a running median of y over a range of x. I've photoshoped in an example: Modified Scatter Plot Specifically, I need the median for data points in bins of 1 unit along the x axis between two values (this range will vary between many plots, but I can manually adjust it). I appreciate any tips that can point me in the right direction.