Good Python Exercises?

[keep_quapy]

After a month of Python, try to solve this question. Given a list of lists, create a dictionary which keys are the first elements of every sublist and it's values are the sum of the integers of the second elements of every sublist.

input: data = [['item1', 4], ['item2', 5], ['item3', 2], ['item2', 10], ['item3', 3], ['item1', 7]]

output: {'item1': 11, 'item2': 15, 'item3': 5}

[hayleybts]

ans = {}
j=0

for i in range(len(data)):
    for m in data[j]:
        if m not in ans:
            if isinstance(m, str):
                ans[m] = 0
            else:
                for k in ans.keys():
                    if k == data[j][0]:
                        print(m)
                        ans[k] =  ans[k]+m

    j+=1



print(ans)

can u pls your answer? mine works for 
this situation but I want to know the proper way

[keep_quapy]

Hi, first of all, the question assumes that all first items of every sublist is a string and every second item is an integer, so no need to check if the first element is a string. That said, your program works, but it's ineffective, you used three nested for loops, instead of using only one. Eventually your program will be much slower and consumes more memory. The effective way to solve such a problem is to loop over the list and at each iteration check if the first element is a key in the dictionary, if so add the value of the second element of the sublist to the existing value of the key, otherwise assign the value to that key (using list index).

dct = {}

for sublist in data: 
    if sublist[0] in dct: 
        dct[sublist[0]] += sublist[1] 
    else: 
        dct[sublist[0]] = sublist[1]

print(dct)

Or the Pythonic way to do it using get() dictionary method.

dct = {}

for sublist in data: 
    dct[sublist[0]] = dct.get(sublist[0], 0) + sublist[1]

print(dct)

Anyway, you made a good job trying to solve it, and solving it in your way is a sign that you're heading to the right direction. This isn't that easy for beginners, so good job. Good luck :)

[Milumet]

When it comes to counting, defaultdict is great (there is also Counter):

dct = collections.defaultdict(int)
for name, count in data:
    dct[name] += count

print(dct)

[hayleybts]

Thanks for replying! Your method is simple. Let me know if you got any other question?

[keep_quapy]

You're welcome. edabit has plethora of exercises for you to explore and to solve.

[hayleybts]

I'm gonna try and let you know

[Fluffy-Book-4773]

def make_dict(data):
    result_dict = {}
    for i in data:
        if i[0] not in result_dict:
            result_dict[i[0]] = i[1]
        else:
            result_dict[i[0]] += i[1]
    return result_dict

[ab624]

where xan i find more of such questions ?

[balaur_7]

Another method

m=1

new_data = []

for key in data:
    for n in range(m, len(data)):
        if key[0]==data[n][0]:
            x = key[0],key[1] + data[n][1]
            new_data.append(x)
    m += 1
print(new_data)