Searching within nested list

Question

EDIT

No longer getting list error after making suggested changes but still not returning any matches. Code now:

# all ingredients, represented by numbers: 0= empty selection 1=rice 2=spice 3=vegetable 
allIng = [0,1,2,3]

#Each individual recipe(r)

# Veggie Rice Balls
r1 = (0,1,3)

# Curry Rice
r2 =(0,1,2)

# Herb Sauté
r3 = (0,2,3)

# Vegetable Curry
r4 = (1,2,3)


# all recipes on one list 

allRec = [r1,r2,r3,r4]


#ingredients picked
iP = []
#ingredient count
iC = 1

#User given option to pick up to 3 ingredients
while iC <= 3:
    pitem = int (input ("Pick up to 3 items "))

    if pitem in allIng:
        iP.append(pitem)
        print(iP)
        iC += 1
    else:
        print ("Incorrect entry, please pick again")

#sort list
iP.sort()
tuple(iP)

#compare iP to allRec looking for matches
if iP in allRec:

    matches = set (iP) & set(allRec)
    print ("Matches:",matches)

Trying to get it print out which recipe matched and if possible tag the name of the recipe itself.

set(allRec) is set([r1,r2,r3,r4]) which is set([[0,1,3], ...]). It is reading r1 as [0, 1, 3], and that's a list which isn't hashable and therefore not a valid member of a set. — jonrsharpe
– jonrsharpe, Commented Jan 19, 2020 at 11:52
So I'm definitely going to blame this on my lack of understanding. But why does it work if I use set (iP) & set (r1)? Is r1 then being seen as a individual elements vs a list as a whole? — Juan
– Juan, Commented Jan 19, 2020 at 12:04
Because set(r1) is set([0, 1, 3]), which is making a set containing integers. Integers are immutable, hashable, valid set members. — jonrsharpe
– jonrsharpe, Commented Jan 19, 2020 at 12:05

Miłosz Wieczór · Accepted Answer · 2020-01-19 12:05:44Z

2

Lists are unhashable since they can be modified during runtime. So instead of lists, try using (non-mutable) tuples - you can define r1 through r4 using parentheses instead of brackets, and convert iP to a tuple after sorting. You can then use sets of tuples with no issues.

answered Jan 19, 2020 at 12:05

Miłosz Wieczór

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3 Comments

Juan Over a year ago

Thank you for looking at this! When I make those changes, I no longer get the error but it is no longer returning match or showing any match. Editing my main post with these changes.

Miłosz Wieczór Over a year ago

Two things to make it work: (1) tuple() does not work in-place, so you need to use iP = tuple(iP); (2) to match the format of allRec (set of tuples), within the loop you need to substitute set(iP) with e.g. set([iP]). As pointed out by @keval-dave below, you can make it work using lists only, but yours is an excellent practice example to highlight some common issues of mutable/immutable objects in Python and handling sets.

Juan Over a year ago

Sorry for the delay but just wanted to say thank you! That did it!

Keval Dave · Accepted Answer · 2020-01-19 12:23:27Z

1

This is because of allRes is a list of the list. Which cannot be converted to the Set.

To get the index of the recipe or recipe you can use the following snippet.

index = allRec.index(iP)
recipe = allRec[index]

You will need no change all the recipes to the set; if ingredients are entered in a different order.

answered Jan 19, 2020 at 12:23

Keval Dave

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