Numpy thermometer encoding

Question

I am trying to use numpy optimized in-built functions to generate thermometer encoding. Thermometer encoding is basically generating n amount if 1\'s in a given len

Answer 1

In [22]: x = [2, 3, 4, 1, 0, 8]

In [23]: length = 8

In [24]: (np.arange(length) < np.array(x).reshape(-1, 1)).astype(int)
Out[24]:
array([[1, 1, 0, 0, 0, 0, 0, 0],
       [1, 1, 1, 0, 0, 0, 0, 0],
       [1, 1, 1, 1, 0, 0, 0, 0],
       [1, 0, 0, 0, 0, 0, 0, 0],
       [0, 0, 0, 0, 0, 0, 0, 0],
       [1, 1, 1, 1, 1, 1, 1, 1]])

Or, create an array of the various lengths of "bars":

In [46]: k = np.arange(length + 1)

In [47]: bars = (k[:-1] < k.reshape(-1, 1)).astype(int)

In [48]: bars

Out[48]: 
array([[0, 0, 0, 0, 0, 0, 0, 0],
       [1, 0, 0, 0, 0, 0, 0, 0],
       [1, 1, 0, 0, 0, 0, 0, 0],
       [1, 1, 1, 0, 0, 0, 0, 0],
       [1, 1, 1, 1, 0, 0, 0, 0],
       [1, 1, 1, 1, 1, 0, 0, 0],
       [1, 1, 1, 1, 1, 1, 0, 0],
       [1, 1, 1, 1, 1, 1, 1, 0],
       [1, 1, 1, 1, 1, 1, 1, 1]])

and use it as a lookup table:

In [49]: bars[x]
Out[49]:
array([[1, 1, 0, 0, 0, 0, 0, 0],
       [1, 1, 1, 0, 0, 0, 0, 0],
       [1, 1, 1, 1, 0, 0, 0, 0],
       [1, 0, 0, 0, 0, 0, 0, 0],
       [0, 0, 0, 0, 0, 0, 0, 0],
       [1, 1, 1, 1, 1, 1, 1, 1]])

In the above code, the preallocated array bars has shape (length+1, length). A more memory efficient representation of bars can be created using:

In [61]: from numpy.lib.stride_tricks import as_strided

In [62]: u = np.zeros(2*length, dtype=int)

In [63]: u[length:] = 1

In [64]: bars = as_strided(u[length-1:], shape=(length+1, length), strides=(u.strides[0], -u.strides[0]))

In [65]: bars
Out[65]: 
array([[0, 0, 0, 0, 0, 0, 0, 0],
       [1, 0, 0, 0, 0, 0, 0, 0],
       [1, 1, 0, 0, 0, 0, 0, 0],
       [1, 1, 1, 0, 0, 0, 0, 0],
       [1, 1, 1, 1, 0, 0, 0, 0],
       [1, 1, 1, 1, 1, 0, 0, 0],
       [1, 1, 1, 1, 1, 1, 0, 0],
       [1, 1, 1, 1, 1, 1, 1, 0],
       [1, 1, 1, 1, 1, 1, 1, 1]])

Then bars is a view of the one-dimensional array u, and it only uses 2*length integers.