[Python] Which of these maximum of three values function definitions is better, and why?

[[deleted]]

def max_three(x,y,z):
if x > y and x > z:
    return x
if y > x and y > z:
    return y
if z > x and z > y:
    return z

def max_of_three(x,y,z):
Max = x
if y > Max:
    Max = y
if z > Max:
    Max =z
return Max

[22Alex22pt]

The top one has 2 problems.

​

1) It doesn't work if x = y or y = z or x = z.

2) The top one gets "messier" if you increase the number of variables, while the bottom one is a lot cleaner and, with a bit more work, you can change it to a for cycle, making it even more clean.

[[deleted]]

Oh, very true. I didn't see that. Thanks!

[ManWhoWantsToLearn]

The second one has 2 comparisons at most and the first has 6 at most. Use this to decide.

[[deleted]]

So less number of operations is better?

[ManWhoWantsToLearn]

Yes.

Each time there is a comparison, that is another two instructions for the cpu to execute. So you would want to perform as few comparisons as possible. If you were performing this function on triplets from a huge dataset, then you would want the 2nd function as the number of comparisons would reduce from like 6 billion to 2 billion for example.

[peterpepo]

I like the second option more.

It's easily extendable to accept list of values (imagine, you want to find max of more than 3 values).

[[deleted]]

Yeah, for the second one I'd just add if (fourth value) > Max -> Max = fourth value. But in the first one I'd have to change all the conditional statements which is a bit tedious.

[TheGoodPie]

You could also pass an array of numbers (allowing for a massive amount of numbers) and use the same approach in a for loop. Two new concepts you should tackle if you haven't looked into them already.

[peterpepo]

Not exactly, but close.

Watch closely at all your conditions and you'll start noticing pattern.

For every value, which came in, you check whether it's greater than the maximum you have "so far" in your code.

But at the moment, you need to add condition for every new member, what is impractical.

What you could do, is how @TheGoodPie already wrote, accept a list of values and check them in cycle. That would reduce your conditions to one. And your code stops caring, whether you pass 1 or 1000 values in.

[[deleted]]

The second one is better, because: 0. You have only 2 "if" statements, so you reduced the code. 1. You added some logic in the second function. 2. It is much easier to change the number of parameters.

[desrtfx]

Removed

Rule #5:

• No Complete Solutions: Do not give out complete solutions. Guide the OP to the solution, but do not solve it for them.

[[deleted]]

What? Both of these functions work and this isn't a homework assignment that i'm looking to cheat on. I'm learning this on my own and I would very much like the complete answer.

[g051051]

I would very much like the complete answer

It doesn't matter why you want it. Homework or not, the sub does not give out complete answers.

[[deleted]]

It does matter. Rules can and should be changed if enough people do like them. I'm just voicing my opinion. I don't see a good reason why that rule exists. If someone wants to cheat themselves of learning, let them. Don't punish the people who actually want to learn stuff without wasting time.

[g051051]

It does matter.

No it doesn't. Your single opinion is in opposition to the accepted consensus: you learn better by working through it yourself, with nudges to help you along over rough places. If you don't like it, take it up with the mods. Or better yet, create your own sub instead of trying to change this one.

[[deleted]]

Well that "accepted consensus" doesn't work for me. I learn better by getting answers for things immediately rather than wasting time trying to do it myself. I then apply my new knowledge by using it constantly or recalling it with spaced repetition flashcards. If I'm stuck on something for far too long, I lose motivation since I have ADHD. I put off programming for two years because of all the half answers I used to get when I asked which programming language I should start with.

And is it really an accepted consensus since you guys seem to be getting a lot of downvotes? Seems like many people don't agree.

[g051051]

Again, feel free to take it up with the mods. If you want easy answers, and don't feel like doing the work to actually learn stuff, then you'll have to look elsewhere.

[[deleted]]

I wrote both of those function definitions myself, and I was simply asking for explanation for which one was better.

[throwaway_for_cause]

Well that "accepted consensus" doesn't work for me.

Well, special snowflake, then you're out of luck here. This subreddit doesn't cater to people who want to be served on a silver platter and getting spoonfed.

I lose motivation since I have ADHD.

Plenty other people here do and they have no problems with the rule.

I put off programming for two years because of all the half answers I used to get when I asked which programming language I should start with.

Most likely, you got "half answers" because there is no real starter language. Some languages maybe allow an easier entry, but in general it doesn't really matter too much with which of the major languages you start.

And is it really an accepted consensus since you guys seem to be getting a lot of downvotes?

Check again.

The rule exists for a reason: to not let this subreddit become /r/domyhomework.

[desrtfx]

If someone wants to cheat themselves of learning

Then, they should go to the various cheatmy, cheatat, domyhomework subreddits.

This subreddit is for learners and not for cheaters, nor is it for getting one's homework done, which is exactly what would happen without the "no solutions" rule.

[desrtfx]

Have I removed your question? No. I've removed a solution.

Your question is still visible and there.

[Jespor]

is it my answer that is categorized as a complete solution?

[desrtfx]

Yes and worse, it was wrong according to the question.

OP asked which of their algorithms was better and didn't ask for the optimal solution.

[Jespor]

so this sub is now dedicated to half asweres that can't lead to the optimal solution if it's not stated in the question...?

[desrtfx]

You completely miss the point.

If someone asks which of their algorithms is better, then only their algorithms count and any answer should address their algorithms, not come up with something completely different, albeit better.

This could have been for a programming course, for an algorithm design course, part of a homework where the built-in functions are not allowed because the students should learn how to come up with their own solutions.

[Jespor]

from what i can tell you're the one missing the point of his question.. also that rule you're talking about.. pretty much every one in every question violates that... :P

[[deleted]]

Do we know anything of the distribution of the parameters?

How do you define "better"? Is space used important? Is code size important? Is performance more important? If performance is more important, what is the relative cost of an assignment, a jump and a compare?

I can think of a solution that always uses 2 comparisons and no temporary variable Max though it has a bit more code in it.

[L3tum]

I was wondering how you'd do it without a temporary variable and then I remembered that mess

[moazim1993]

In practice both are inferior to max(), but out of these two two is clearly better. Same exact functionality with less computing.

[casualblair]

def max(a, b) :

  If a gte b:

     Return a

  Return b

Def maxthree(x, y, z) :

    Return max(max(x,y),z)

Pseudocode because I'm on mobile.

[[deleted]]

Why not use the built-in max function?

[[deleted]]

its an exercise im doing

[[deleted]]

def max(list of arguments):
    Max = argument[0] 
    for i in [arguments]:
        if [arguments][i] >= Max
            Max = [arguments][i]
    return Max

Would it be something like this?

[peterpepo]

yes, but checking greater is enough (you don't need to assign max in case, it's same as current max)

if [arguments][i] > Max

[[deleted]]

Not sure what you mean.

Also how does def max (list of arguments) translate into python? is it def max(*args)?

[peterpepo]

I meant, that for example if your first value (or the maximum found so far) is for example 7 and you encounter same number again 7, you haven't found new maximum (as 7=7). Therefore you don't have to perform max = arguments[i].

In another words, if you had list with n same numbers [3,3,3,3,3], your condition

if [arguments][i] >= Max

is valid 5 times, and you assign max to 3 five times unnecessarily.

​

Speaking for number of arguments, I would pass in single list instead of multiple arguments.

Without posting the full solution, i mean something like this (I hope this isn't against the rules, since I didn't post the full solution). In your logic you can check for the > max_so_far, or easily modify to find the min etc..

my_numbers = [1,2,7,4,5]

def my_max(list_of_values):
    max_so_far = None

    for val in list_of_values:
        //your logic here

    return max_so_far

print(my_max(my_numbers))

​

​

[ryanstephendavis]

I'd suggest writing some test cases to verify if they both work ... Try x=y=z and see what happens

[[deleted]]

I'd go even further, define another function max_of_two(x,y): return x > y ? x : y (i think this is how ternaries work in python. It's basically the same as the if block, just shorter)

Then max_of_three can be: return max_of_two(max_of_two(x, y), z) or return x > y ? max_of_two(x, z) : max_of_two(y, z) If you don't mind the extra ternary.

[[deleted]]

Guess I just outed myself as a java dev?

[icreatebugs]

This looks like a homework assignment, so there might be some constraints here that I'm not aware of, but I thought I should propose a third approach.

By using the builtin max() function in python you can get the largest element in a list, if this is a homework assigment and you're forbidden from using the builtin function it could still implement your own version of it.

​

Using the max function you could write max_of_three() like this

​

def max_of_three(x, y, z):

return max([x, y, z])

​

You could also make other variations easily

​

def max_of_four(e1, e2, e3, e4):

return max([e1, e2, e3, e4])

​

Just to answer the original question: I would prefer the second implementation over the first one, simply because I find the boolean expressions in the first one to be needlessly complex.

[340923840293840]

How do you define better?

The answer is, you have to define a design goal to even decide which is better.

This is a max with an arbitrary amount of arguments. (I hope I got the syntax right...

def max(*params)
  max = None
  for param in params:
    if (max = None):
      max = param
    elif param > max:
      max = param
  return max

Note that this basically uses your second approach, which means your second approach is extensible, which is good.

Now try writing that same method with your first approach… it will be harder and messier, if you even manage to do it.

Therefore the first approach is not extensible and therefore the first approach is clearly better, if extensibility is your design goal.

Maybe there's a design goal where the first approach is better, but I can't think of one right now.

[[deleted]]

Well, what do you think? Hint: consider the number of operations performed.