Large list, find all minima of list (python)

Question

Given a large list of fluctuating values, how do you determine all local min values? Not using numpy. Local minimum means all values in a list that are the troughs

Answer 1

I'm a big fan of iterating over these problems in stages.

l = [23, 8, -7, -7, 57, 87, 6]

# Remove identical neighbors
# l becomes [23, 8, -7, 57, 87, 6]
l = [x for x,y in zip(l[0:], l[1:]) if x != y] + [l[-1]]

# Append positive infinity to both endpoints
# l becomes [inf, 23, 8, -7, 57, 87, 6, inf]
l = [float("inf")] + l + [float("inf")]

# Retain elements where each of their neighbors are greater than them.
# l becomes [-7, 6]
l = [y for x, y, z in zip(l[0:], l[1:], l[2:]) if x > y < z]

Answer 2

Here You can easily understand array sorting...

my_array = [10,20,30,5,1,8,2,14,6,29] #main array
if len(my_array) > 0:
    my_array.sort() #sorting array(min to max)
    min = my_array[0] #after sorting get min value
    print(min) #print min value
else:
    print("array is empty")

Answer 3

def local_min(ys):
    return [y for i, y in enumerate(ys)
            if ((i == 0) or (ys[i - 1] >= y))
            and ((i == len(ys) - 1) or (y < ys[i+1]))]


>>> local_min([23, 8, -7, 57, 87, 6])
[-7, 6]
>>> local_min([23, 6, 6, 6, 42])
[6]
>>> local_min([6, 6, 4])
[4]