问题描述
目标是创建一个数组，但要满足(x=>y) and (y=>z)的条件.
The objective is to create an array but by fulfilling the condition of (x=>y) and (y=>z).
一种天真的方法是使用嵌套的for循环，如下所示
One naive way but does the job is by using a nested for loop as shown below
tot_length=200
steps=0.1
start_val=0.0
list_no =np.arange(start_val, tot_length, steps)
a=np.zeros(shape=(1,3))
for x in list_no:
for y in list_no:
for z in list_no:
if (x>=y) & (y>=z):
a=np.append(a, [[x, y, z]], axis=0)
虽然没有抛出内存需求问题，但执行时间明显变慢.
While no memory requirement issue was thrown, but the execution time is significantly slow.
可以考虑的其他方法是使用下面的代码代码.然而，只要tot_length 小于100，该提案才能完美运行.更重要的是，内存问题出现在此处
Other approach that can be considered is by using the code code below. Yet the proposal only able to work flawlessly as long as tot_length is less than 100. More than that, memory issue arise as reported here
tot_length=200
steps=0.1
start_val=0.0
list_no =np.arange(start_val, tot_length, steps)
arr = np.meshgrid ( *[list_no for _ in range ( 3 )] )
a = np.array(list ( map ( np.ravel, arr ) )).transpose()
num_rows, num_cols = a.shape
a_list = np.arange ( num_cols ).reshape ( (-1, 3) )
for x in range ( len ( a_list ) ):
a=a[(a[:, a_list [x, 0]] >= a[:, a_list [x, 1]]) & (a[:, a_list [x, 1]] >= a[:, a_list [x, 2]])]
感谢任何可以平衡整体执行时间和内存问题的建议.我也欢迎任何使用 Pandas 的建议，如果这能让事情顺利的话
Appreciate for any suggestion that can balance the overall execution time as well as memory issue. I also welcome for any suggestion using Pandas if that should make thing work
为了确定提议的输出是否产生了预期的输出，以下参数
To determine whether the proposed output produced the intended output, the following parameter
tot_length=3
steps=1
start_val=1
应该产生输出
1 1 1
2 1 1
2 2 1
2 2 2
推荐答案
这样的事情有用吗?
tot_length=200
steps=0.1
list_no = np.arange(0.0, tot_length, steps)
x, y, z = np.meshgrid(*[list_no for _ in range(3)], sparse=True)
a = ((x>=y) & (y>=z)).nonzero()
这仍然会为中间布尔数组使用 8GB 的内存，但避免重复调用 np.append，因为它们很慢.
This will still use 8GB of memory for the intermediate array of booleans, but avoids repeated calls to np.append which are slow.
这篇关于如何使用 Numpy 有效地创建条件列数组?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！