Python tricks

tricks.py

#Ref: http://akuederle.com/create-numpy-array-with-for-loop
import numpy as np
n_results_per_iter = 4
result_array = np.empty((0, n_results_per_iter))
for iter in [1,2,3]:
    result_this_iter = np.array([0,1,2,3])
    result_array = np.append(result_array, [result_this_iter], axis=0)
    
  
#Slicing rows and columns from a matrix simultaneously. The key is to use broadcasting.
#https://stackoverflow.com/questions/22927181/selecting-specific-rows-and-columns-from-numpy-array
M = np.random.randint(10,size=(10,10))
rows = np.random.randint(M.shape[0],size=2)
cols = np.random.randint(M.shape[1],size=3)
M[np.ix_(rows, cols)]