45 lines
1.1 KiB
Cython
45 lines
1.1 KiB
Cython
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cimport cython
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cimport numpy as np
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import numpy as np
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cdef class ArrayBuilder(object):
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"""Helper class to incrementally build a 1-d numpy.ndarray"""
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# Or: let's reinvent the wheel!
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GROWTH_FACTOR = 1.5
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cdef Py_ssize_t _nelems
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cdef object _arr # object because we don't know the dtype statically
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def __init__(self, dtype, initial_capacity=256):
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assert self.GROWTH_FACTOR > 1
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assert initial_capacity >= 2
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self._arr = np.empty(initial_capacity, dtype=dtype)
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self._nelems = 0
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def __len__(self):
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return self._nelems
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@cython.boundscheck(False)
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def append(self, x):
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"""Append a single value.
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Complexity: amortized O(1).
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"""
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if self._nelems == self._arr.size:
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self._grow()
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self._arr[self._nelems] = x
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self._nelems += 1
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def get(self):
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"""Return the constructed array.
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Don't use an ArrayBuilder after calling this method.
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"""
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self._arr.resize(self._nelems)
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return self._arr
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cdef _grow(self):
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self._arr.resize(self._arr.size * self.GROWTH_FACTOR)
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