如果你想就地对 numpy 数组应用数学运算,你可以简单地使用标准的就地运算符+=
, -=
, /=
等等。例如:
>>> def foo(a):
... a += 10
...
>>> a = numpy.arange(10)
>>> a
array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
>>> foo(a)
>>> a
array([10, 11, 12, 13, 14, 15, 16, 17, 18, 19])
这些操作的就地版本启动速度要快一些,特别是对于较大的阵列:
>>> def normalize_inplace(array, imin=-1, imax=1):
... dmin = array.min()
... dmax = array.max()
... array -= dmin
... array *= imax - imin
... array /= dmax - dmin
... array += imin
...
>>> def normalize_copy(array, imin=-1, imax=1):
... dmin = array.min()
... dmax = array.max()
... return imin + (imax - imin) * (array - dmin) / (dmax - dmin)
...
>>> a = numpy.arange(10000, dtype='f')
>>> %timeit normalize_inplace(a)
10000 loops, best of 3: 144 us per loop
>>> %timeit normalize_copy(a)
10000 loops, best of 3: 146 us per loop
>>> a = numpy.arange(1000000, dtype='f')
>>> %timeit normalize_inplace(a)
100 loops, best of 3: 12.8 ms per loop
>>> %timeit normalize_copy(a)
100 loops, best of 3: 16.4 ms per loop