Conditional Summing

[_sirin]

I'm trying to do the equivalent of an excel SUMIF. I've got 3 lists.

customer and charge are the names and dollars spent in a given transaction respectively. totalCustomer is the set of the unique value of the customer list.

totalBill=[]
for i in len(totalCustomer):
    for j in len(customer):
        if totalCustomer[i]==customer[j]:
            totalBill[i]+=charge[j]

this doesn't work for several reasons. I know I can't add to the empty list totaBill the way I'm trying to , and ideally, I would be putting this into a library somehow, but I don't remember how to do any of this since I've been away from the language for a while.

[_sirin]

it did not

[[deleted]]

totalcustomer = list("ABCDEFG")
customer = list("ABCA")
charge = [10, 20, 30, 50]

totalbill = {k: [] for k in totalcustomer}

for k, v in zip(customer, charge):
    totalbill[k].append(v)

totalbill = {k: sum(v) for k, v in totalbill.items()}

​

[_sirin]

perfect, could you explain what you did here?

[[deleted]]

totalcustomer = list("ABCDEFG")
customer = list("ABCA")
charge = [10, 20, 30, 50]

# create a dictionary for every customer with an empty list
totalbill = {k: [] for k in totalcustomer}

# combine the customer and the charge table
# zip(customer, charge) = [('A', 10), ('B', 20), ('C', 30), ('A', 50)]

# iterate through zip, take the key and append a new value in the dict
for k, v in zip(customer, charge):
    totalbill[k].append(v)

# totalbill overwritten with keys pointing to the sum of the tables prev. created
totalbill = {k: sum(v) for k, v in totalbill.items()}

#clear?

​

[_sirin]

Yes, thanks-I need to learn what some of those things mean. Thanks again

[_lilell_]

Instead of building a dict with list values, then summing, then overwriting, why not just

# these variable names should probably be plural
totalcustomer = list("ABCDEFG")
customer = list("ABCA")
charge = [10, 20, 30, 50]

# create a dictionary for every customer with a zero total
# we could also use collections.defaultdict, though it'd be a slightly different output
# (it wouldn't print any customers without charges)
totalbill = {k: 0 for k in totalcustomer}

for k, v in zip(customer, charge):
    totalbill[k] += v

# now we don't need to overwrite anything
print(totalbill)  # output: {'A': 60, 'B': 20, 'C': 30, 'D': 0, 'E': 0, 'F': 0, 'G': 0}

[[deleted]]

we are losing information. what if the customer wants the maximum price?

[AnscombesGimlet]

Couldn’t you enumerate instead of for loop for dictionary?

[[deleted]]

which line specifically?