CODEWITHSUNDEEP
pythonlistmin
Jsg91
Jsg91

Reputation: 465

Minimum of a list up to that point in the loop

I have a list of tuples containing 2 numbers like below. I essentially need to know the current minimum for how far into the list I am, hopefully outputting something like l2.

l = [(30, -182), (55, -160), (72, -143), (92, -183)] 
l2 = [(30, -182), (55, -182), (72, -182), (92, -183)]

I've tried using enumerate but keep encountering:

ValueError: min() arg is an empty sequence

The code I'm using so far:

for i,(ss,en) in enumerate(sdat):
    print ss, min(x[1] for x in sdat[:i])

Any help is greatly appreciated!

Upvotes: 0

Views: 39

Answers (1)

Veedrac
Veedrac

Reputation: 60127

Well, you're getting a bit confused.

for i,(ss,en) in enumerate(sdat):

You don't need indexes as long as you can keep history, so there's your first hint.

    print ss, min(x[1] for x in sdat[:i])

You're rerunning min (incorrectly) every time; this is a lot of work to compare two numbers.

Just do this manually:

sdat = [(30, -182), (55, -160), (72, -143), (92, -183)] 

if sdat:
    ss, en = sdat[0]

for ss, new_en in sdat:
    if new_en < en:
        en = new_en
    print((ss, en))

#>>> (30, -182)
#>>> (55, -182)
#>>> (72, -182)
#>>> (92, -183)

Also, to prove that I'm supeh functional and stuff, here's what I'd actually do:

from itertools import accumulate

def oddmin(a, b):
    return b[0], min(a[1], b[1])

accumulate(l, oddmin)

Requires 3.3 and up, so this won't work for Jsg91.

Upvotes: 3

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