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"""
Helper module containing functions that operate on numpy arrays.
"""
import numpy as np
def calc_repeats(delay):
"""
Calculates offsets corresponding to an array, where repeated values are
subsequently numbered, i.e. if there n identical values, the returned array
will have values from 0 to n-1 at their positions.
The code is complex because tricks are needed for vectorisation.
This function is used in the Python `SpikeQueue` to calculate the offset
array for the insertion of spikes with their respective delays into the
queue and in the numpy code for synapse creation to calculate how many
synapses for each source-target pair exist.
Examples
--------
>>> import numpy as np
>>> print(calc_repeats(np.array([7, 5, 7, 3, 7, 5])))
[0 0 1 0 2 1]
"""
# We use merge sort because it preserves the input order of equal
# elements in the sorted output
sort_indices = np.argsort(delay, kind="mergesort")
xs = delay[sort_indices]
J = xs[1:] != xs[:-1]
A = np.hstack((0, np.cumsum(J)))
B = np.hstack((0, np.cumsum(np.logical_not(J))))
BJ = np.hstack((0, B[:-1][J]))
ei = B - BJ[A]
ofs = np.zeros_like(delay, dtype=np.int32)
ofs[sort_indices] = np.array(ei, dtype=ofs.dtype)
return ofs
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