1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
|
# Author: Lars Buitinck <L.J.Buitinck@uva.nl>
# License: BSD-style
cimport cython
cimport numpy as np
import numpy as np
cdef class ArrayBuilder(object):
"""Helper class to incrementally build a 1-d numpy.ndarray"""
# Or: let's reinvent the wheel!
GROWTH_FACTOR = 1.5
cdef Py_ssize_t _nelems
cdef object _arr # object because we don't know the dtype statically
def __init__(self, dtype, initial_capacity=256):
assert self.GROWTH_FACTOR > 1
assert initial_capacity >= 2
self._arr = np.empty(initial_capacity, dtype=dtype)
self._nelems = 0
def __len__(self):
return self._nelems
@cython.boundscheck(False)
def append(self, x):
"""Append a single value.
Complexity: amortized O(1).
"""
if self._nelems == self._arr.size:
self._grow()
self._arr[self._nelems] = x
self._nelems += 1
def get(self):
"""Return the constructed array.
Don't use an ArrayBuilder after calling this method.
"""
self._arr.resize(self._nelems)
return self._arr
cdef _grow(self):
self._arr.resize(self._arr.size * self.GROWTH_FACTOR)
|
