find runs of constant value, returning their indices

mask2runs.py

import numpy as np

def mask2runs(mask):
  '''
  mask2runs
 
  Turns a boolean array into an array of indices indicating the start and end indices of each run of 1's.
  '''
  runflip = np.nonzero(mask[1:] ^ mask[:-1])[0]+1 
  runflip[1::2] -= 1 # Note that the prior step returns end indices as the end of a run plus 1
 
  # if the last run was a run of 1's, count the last epoch as the end of the run
  # similarly if the first bit started a run of 1's
  if mask[-1]: runflip = np.r_[runflip,len(mask)]
  if mask[0]: runflip = np.r_[0,runflip]
 
  return runflip[::2], runflip[1::2]