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它似乎從int數組中減去float32數字默認情況下會生成float64數組。有沒有辦法繞過這一點,並獲得float32作爲結果的數據類型?如何爲NumPy中的算術運算指定結果數據類型?
numpy.subtract不允許指定dtype參數。
實現此目的的唯一方法是將int數組轉換爲float32之前,有效地減去兩個似乎相當慢的float32數組。這是它應該的方式嗎?
示例代碼:
import time
import numpy as np
if __name__ == '__main__':
# some int32 array
a = np.arange(1e7)
print('a.dtype={}'.format(a.dtype)) # int32
# subtraction with a python float
t0 = time.clock()
b = a - 5.5
t1 = time.clock()
print('b.dtype={}, took {}s'.format(b.dtype, t1 - t0)) # float64
# a numpy float32
c = np.array(5.5, dtype=np.float32)
print('c.dtype={}'.format(c.dtype)) # float32
# subtraction with the numpy float32
t0 = time.clock()
d = a - c
t1 = time.clock()
print('d.dtype={}, took {}s'.format(d.dtype, t1 - t0)) # float64! why not float32
# convert the int32 to float32
e = a.astype(dtype=np.float32)
print('e.dtype={}'.format(e.dtype)) # float32
# subtract two float32 array
t0 = time.clock()
e = a.astype(dtype=np.float32)
f = e - c
t1 = time.clock()
print('f.dtype={}, took {}s'.format(f.dtype, t1 - t0)) # float32 (finally)
打印
a.dtype=float64
b.dtype=float64, took 0.0229595559008s
c.dtype=float32
d.dtype=float64, took 0.0223958136306s
e.dtype=float32
f.dtype=float32, took 0.0334388477586s
手動轉換爲FLOAT32之前似乎比自動轉換爲float64慢。
嘗試這是字面上我的第一個想法,我想我已經嘗試過。但似乎我沒有。還要感謝promote_types和result_type。 – Trilarion