Python: Removing duplicates from a list

Question

After reading some data from a file and sorting through it, I get this.

[['John', 1], ['Lisa', 2], ['Carly', 2], ['Zacharry', 1], ['Brian', 3], ['John', 5], ['Carly', 2]]

How can I removed the duplicates while also adding the values they have so my output would look like this

[['John', 6], ['Lisa', 2], ['Carly', 4], ['Zacharry', 1], ['Brian', 3]]

I've been able to isolate the duplicates on their own with the total sum of data, however I have no idea how to get my desired output.

Note: Order of the list is important in my case and that my data stays in a list

When I've isolated the duplicates I get this output:

[['John', 6], ['Carly', 4]]

My Code:

def create_bills(filename, capacity):
fob = open(filename)
newlst = list()
for line in fob:
    a = line.split(" $")
    b = [a[0], int(a[1])]
    newlst.append(b)
print(newlst)
newlst2 = list()
for i in range(len(newlst)):
    n = i + 1
    while n < len(newlst):
        if newlst[i][0] == newlst[n][0]:
            newlst2.append([newlst[i][0], (newlst[i][1] + newlst[n][1])])
        n += 1
newlst3 = list()
for i in range(len(newlst)):
    pass
print(newlst2)

Thank you!

Answer 1

You can use a dict, more specifically an OrderedDict to keep track of the counts:

from collections import OrderedDict
lst = [['John', 1], ['Lisa', 2], ['Carly', 2], ['Zacharry', 1], ['Brian', 3], ['John', 5], ['Carly', 2]]
d = OrderedDict()
for k, v in lst:
    if k not in d:
        d[k] = v
    else:
        d[k] += v
print map(list, d.items())
#[['John', 6], ['Lisa', 2], ['Carly', 4], ['Zacharry', 1], ['Brian', 3]]

Code readability issue aside, it's important to note that it takes O(N^2) complexity if you maintain the counts in a list, like what the original code is doing. The dictionary approach takes O(N).

Answer 2

This should give your answer.

def out(a):
    x={name:0 for name,value in a}
    for name,value in a:
        x[name]=x[name]+value

    final=[]
    for i in a:
        if (i[0],x[i[0]]) not in final:
            final.append((i[0],x[i[0]])) 
    return final

The output is [('John', 6), ('Lisa', 2), ('Carly', 4), ('Zacharry', 1), ('Brian', 3)]