How to use reduce on dictionary in Python

Question

I have two classes - Item and AIShoppingCart (which has dictionary, for example {"milk" : Item(2, 2.28, 1)}). I have to find the most likable item from my cart using reduce and I am not allowed to use max(). Unfortunately, my program throws an error

<lambda>() takes 1 positional argument but 2 were given

class Item:
def __init__(self,quantity,price,likable):
    self.quantity = quantity
    self.price = price
    self.likable = likable

class AIShoppingCart(ShoppingCart):
def __init__(self,items):
    super().__init__(items)
def add_item(self,name,quantity,price):
    if name in self.items:
        self.items[name].likable+=1
        self.items[name].quantity+=quantity
    else:
        items[name]=Item(quantity,price,1)

def findMostLikable(self):
    return reduce(lambda x:self.items[x].likable>1, self.items)

How should I use reduce?

xjcl · Accepted Answer · 2020-11-15 22:45:16Z

3

Please look up the documentation for reduce. If you do reduce(f, [a, b, c, d]) this will essentially be applied as f(f(f(a, b), c), d) -- so reduce essentially takes 2 elements at a time and reduces them to 1.

In your case the reduce function just has to pick the greater element by value:

return reduce(lambda a, b: a if a[1].likable >= b[1].likable else b,
              self.items.items())

The .items() function gets your dictionary's key-value pairs as a list of tuples, whose value I get using a[1]/b[1] -- the returned result is a key-value-tuple.

If you just want the maximum value, without caring about the keys:

return reduce(lambda a, b: a if a.likable >= b.likable else b,
              self.items.values()).likable

edited Nov 15, 2020 at 22:45

answered Nov 15, 2020 at 20:55

xjcl

15.7k8 gold badges87 silver badges108 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Enchantres Over a year ago

I get it, but I cannot solve how to compare the items by the likable property.

xjcl Over a year ago

That would be a[1].likable, I'll update my answer, sorry about that

Enchantres Over a year ago

I am getting the following error ('eggs', <Item.Item object at 0x000001EA58C43908>) But yes, it almost works. The output should be eggs's likable count.

xjcl Over a year ago

That's not an error, that's the result. You can add [1].likable to the very end to get just the value, but in that case you can just iterate over the .values() directly. I'll update my answer.

Collectives™ on Stack Overflow

How to use reduce on dictionary in Python

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related