python - Python 或 R，有效地将时间序列划分为之字形

Question

如果我有清单

l = [0, 0, 1, 2, 2, 2, 1, -1, -1, -1, 0]

我希望获得三个之字形，一个之字形定义为局部最大值（可以是高原）和最小值（可以是山谷），如下图，有3个之字形，A，B，C而A和B在高原重叠，B和C在山谷重叠

A = [0, 0, 1, 2, 2, 2]
B = [2, 2, 2, 1, -1, -1, -1]
C = [-1, 0]

Answer 1

一般 Python 中的一个解决方案，注意l可以是任何迭代器，并且它只被扫描一次。

l = [0, 0, 1, 2, 2, 2, 1, -1, -1, -1, 0]

def zigzag(l):
    if not l:
        return []

    last = l[0]

    # the elements in current rise    
    current_rise = []

    # the elements in current drop
    current_drop  = []

    # return value
    zigzags = []

    # iterate over elements
    for i in l:
        # if we are growing...
        if i > last:
            # and the current_drop is longer than
            # current rise, then we just stopped a drop
            if len(current_drop) > len(current_rise):
                zigzags.append(current_drop)

            # in any case, a new drop can start here.
            current_drop = [i]

        else:
            # else just accumulate a current drop
            current_drop.append(i)

        # same for the other direction
        if i < last:
            if len(current_rise) > len(current_drop):
                zigzags.append(current_rise)

            current_rise = [i]

        else:
            current_rise.append(i)

        last = i

    # add the final segment    
    if len(current_rise) > len(current_drop):
        zigzags.append(current_rise)
    else:
        zigzags.append(current_drop)

    return zigzags

print zigzag(l)
# result [[0, 0, 1, 2, 2, 2], [2, 2, 2, 1, -1, -1, -1], [-1, -1, -1, 0]]