将多个函数与相关数组结合使用Numpy Python [英] using multiple functions with correlated arrays Numpy Python

问题描述

假定下面的函数根据 Set 和 Numbers 计算 Uval 和 Lval 函数.对于前两个数字，与 U 和 52599 相关，而与 L 和 52550 相关，因为第二个数字数字具有标签 L 的标签，将使用 Lval 公式.前一个函数是 previous = numbers [1:] ，而当前函数是 current = numbers [:-1] .因此(52550-52599)/52550 * -100 将是前两个数字的计算.这些方程应该一直计算到 Set 和 Numbers 数组的末尾.但是代码下面给了我错误， Set 和 Numbers 数组的长度均为15.

The function below is supposed compute either the Uval and Lval functions in accordance to Set and Numbers. For the first two numbers U and 52599 are in relation and L and 52550 are in relation, since the second number has the label L the Lval equation is used. The previous number is function is previous = numbers[1:] and the current function is current = numbers[:-1]. So (52550 - 52599)/52550 * -100 will be the computation for the first two numbers. The equations are supposed to be computed until the end of the Set and Numbers arrays. However the code gives me the error down below, both the Set and Numbers array have the length of 15.

功能:

Set = np.array(['U', 'L', 'U', 'L', 'U', 'L', 'U', 'L', 'U', 'L', 'U', 'L', 'U', 'L', 'U'])
Numbers = np.array([ 52599, 52550, 53598, 336368, 336875, 337466, 338292, 356587, 357474, 357763, 358491, 358659, 359041, 360179, 360286])
Lval = (Numbers[:-1] - Numbers[1:])/Numbers[:-1] * -100
Uval = (Numbers[1:] - Numbers[:-1])/ Numbers[1:] * -100
Numbers * np.where(Set == 'U', Uval, Lval)

错误输出:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-12-3ddad609950b> in <module>
      4 Uval = (Numbers[1:] - Numbers[:-1])/ Numbers[1:] * -100
      5 print(len(Set))
----> 6 Numbers * np.where(Set == 'U', Uval, Lval)

<__array_function__ internals> in where(*args, **kwargs)

ValueError: operands could not be broadcast together with shapes (15,) (14,) (14,)

推荐答案

您的切片符号没有按照您的想象做:

your slice notation isn't doing what you think it is:

in: Numbers[:-1] 

对数组中的元素进行 not 移位1.它将所有元素向上移动，但不包括最后一个元素.输出为:

does not shift elements in the array by 1. It takes all elements up to but not including the last element. The output is:

in: Numbers[:-1] 
out: array([ 52599,  52550,  53598, 336368, 336875, 337466, 338292, 356587,
   357474, 357763, 358491, 358659, 359041, 360179])

那是Numbers中除最后一个360286之外的所有元素.

That is every element in Numbers except for the last, 360286.

您需要使用np.roll()函数将元素移动一个.但这会将最后一个元素滚动到前面:

You need to use the np.roll() function to shift elements by one. This will roll the last element to the front though:

in: np.roll(Numbers, 1)
out: array([360286,  52599,  52550,  53598, 336368, 336875, 337466, 338292,
   356587, 357474, 357763, 358491, 358659, 359041, 360179])

所以您必须处理最开始和最后一个数字的极端情况，例如您的数组长度为15，因此对于L或U您只能获得14个新元素.

so you have to handle the edge case of what to do with the very first and very last numbers, e.g. your arrays are length 15, so you can only get 14 new elements for either L or U.

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