I'm using somoclu
to produce an emergent Self-Organising Map of some data. Once I have the BMUs (Best Matching Units) I'm performing a Delaunay Triangulation on the co-ordinates of the BMUs in order to find each BMU's neighbours in the SOM.
In the following snippet of Python, is there a more Pythonic version of the a == c and b == d
conditional? In other words, how can I compare bmu
and point
directly without splitting out the separate co-ordinates?
points = np.unique(np.array(som.bmus), axis = 0)
for idx, bmu in enumerate(som.bmus):
a, b = bmu
for point_idx, point in enumerate(points):
c, d = point
if a == c and b == d: # More Pythonic version of this line?
print (idx, point_idx)
break
Approach #1
We are working with NumPy arrays, so we can leverage broadcasting
for a vectorized solution -
ar = np.array(som.bmus)
points = np.unique(ar, axis = 0)
mask = (ar[:,0,None]==points[:,0]) & (ar[:,1,None]==points[:,1])
indices = np.argwhere(mask)
Approach #1-G
One more compact way to get mask
, which covers for a generic no. of columns in ar
, would be -
mask = (ar[:,None] == points).all(axis=2)
Approach #2
Another memory-efficient approach for generic no. of cols would be with views
and np.searchsorted
-
# https://stackoverflow.com/a/45313353/ @Divakar
def view1D(a, b): # a, b are arrays
a = np.ascontiguousarray(a)
b = np.ascontiguousarray(b)
void_dt = np.dtype((np.void, a.dtype.itemsize * a.shape[1]))
return a.view(void_dt).ravel(), b.view(void_dt).ravel()
n = len(ar)
indices = np.empty((n,2),dtype=int)
indices[:,0] = np.arange(n)
a,b = view1D(ar, points) # ar, points from app#1
indices[:,1] = np.searchsorted(b, a)