Solving max delta within an array

Question

I'm having issues determining my maximum value calculated in my for loop. I'm using Python to evaluate an array to determine the maximum delta in a sequence i.e. maximum value i+1-i.

I'm having two issues:

SyntaxError: 'return' outside function
I don't know how to pull the largest calculated iterated value from my for loop

Tried having other variables to compare largest values etc

prices=[7,1,5,3,6,4]
profit_loss=0
for i in range(0,len(prices)-1):
        profit_loss=prices[i+1] - prices[i]
        return(profit_loss)
        print(profit_loss)

Maximum value should be 4 and the results of my print are below:

-6
4
-2
3
-2

This question is unique because I am looking to understand why the return function is not necessary.

Possible duplicate of [Finding the largest delta between two integers in a list in python](https://stackoverflow.com/questions/3428769/finding-the-largest-delta-between-two-integers-in-a-list-in-python) — Aaditya Maheshwari, Dec 27 '18 at 03:17

jpp · Accepted Answer · 2018-12-27T03:14:07.340

You can't return outside a function. In fact, you don't need return here:

prices = [7,1,5,3,6,4]
profit_loss = -float('inf')

for i in range(len(prices)-1):
    change = prices[i+1] - prices[i]
    if change > profit_loss:
        profit_loss = change

print(profit_loss)  # 4

More idiomatic than positional indexing, use zip to iterate elements of prices pairwise:

for i, j in zip(prices, prices[1:]):
    change = j - i
    if change > profit_loss:
        profit_loss = change

More succinctly, use max with a generator comprehension:

profit_loss = max(j - i for i, j in zip(prices, prices[1:]))  # 4

Or use the functional equivalent:

from operator import sub
profit_loss = max(map(sub, prices[1:], prices))  # 4

This is a great explanation. Thank you. – Ramy AS Mar 09 '19 at 14:25 — Ramy AS, Mar 09 '19 at 14:25

score 0 · Answer 2 · answered Dec 27 '18 at 05:12

0

This should work:

prices = [7, 1, 5, 3, 6, 4]
profit_loss = 0
for i in range(0, len(prices)-1):
    res = prices[i+1] - prices[i]
    if res > profit_loss:
        profit_loss = res
print(profit_loss)

answered Dec 27 '18 at 05:12

Partho63

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Solving max delta within an array

2 Answers2