如何向量化包含if语句的函数吗？ [英] How to vectorize a function which contains an if statement?

问题描述

让我们说我们有以下功能：

Let's say we have the following function:

def f(x, y):
    if y == 0:
        return 0
    return x/y

这正常工作与标量值。不幸的是，当我尝试使用numpy的阵列以 X 和是比较ÿ== 0 被视为一个数组操作导致的错误：

This works fine with scalar values. Unfortunately when I try to use numpy arrays for x and y the comparison y == 0 is treated as an array operation which results in an error:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-13-9884e2c3d1cd> in <module>()
----> 1 f(np.arange(1,10), np.arange(10,20))

<ipython-input-10-fbd24f17ea07> in f(x, y)
      1 def f(x, y):
----> 2     if y == 0:
      3         return 0
      4     return x/y

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

<击>我试图用 np.vectorize 但它不会有所作为，在code还是失败，出现同样的错误。 np.vectorize 是一个选项，给出结果我的期望。

I tried to use np.vectorize but it doesn't make a difference, the code still fails with the same error. np.vectorize is one option which gives the result I expect.

这是我能想到的唯一解决办法是使用 np.where 在是阵列像

The only solution that I can think of is to use np.where on the y array with something like:

def f(x, y):
    np.where(y == 0, 0, x/y)

不为标量工作。

有没有更好的方式来写它包含一个if语句的函数吗？它应与标量和数组。

Is there a better way to write a function which contains an if statement? It should work with both scalars and arrays.

推荐答案

您可以使用屏蔽数组将执行师只有在 Y = 0 ：

You can use a masked array that will perform the division only where y!=0:

def f(x, y):
    x = np.atleast_1d(np.array(x))
    y = np.atleast_1d(np.ma.array(y, mask=(y==0)))
    ans = x/y
    ans[ans.mask]=0
    return np.asarray(ans)

这篇关于如何向量化包含if语句的函数吗？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！