从列表列表创建字典

Question

I am working on an online course exercise (practice problem before the final test).

The test involves working with a big csv file (not downloadable) and answering questions about the dataset. You're expected to write code to get the answers. The data set is a list of all documented baby names each year, along with #how often each name was used for boys and for girls. A sample list of the first 10 lines is also given:

Isabella,42567,Girl
Sophia,42261,Girl
Jacob,42164,Boy

and so on.

Questions you're asked include things like 'how many names in the data set', 'how many boys' names beginning with z' etc.

I can get all the data into a list of lists:

[['Isabella', '42567', 'Girl'], ['Sophia', '42261', 'Girl'], ['Jacob', '42164', 'Boy']]

My plan was to convert into a dictionary, as that would probably be easier for answering some of the other questions. The list of lists is saved to the variable 'data':

names = {}
for d in data:
    names[d[0]] = d[1:]

print(names)
{'Isabella': ['42567', 'Girl'], 'Sophia': ['42261', 'Girl'], 'Jacob': ['42164', 'Boy']}

Works perfectly.

Here's where it gets weird. If instead of opening the sample file with 10 lines, I open the real csv file, with around 16,000 lines. everything works perfectly right up to the very last bit. I get the complete list of lists, but when I go to create the dictionary, it breaks - here I'm just showing the first three items, but the full 16000 lines are all wrong in a similar way):

names = {}
for d in data:
    names[d[0]] = d[1:]

print(names)
{'Isabella': ['56', 'Boy'], 'Sophia': ['48', 'Boy'], 'Jacob': ['49', 'Girl']

I know the data is there and correct, since I can read it directly:

for d in data:
    print(d[0], d[1], d[2])

Isabella 42567 Girl
Sophia 42261 Girl
Jacob 42164 Boy

Why would this dictionary work fine with the cvs file with 10 lines, but completely break with the full file? I can't find any

Answer 1

Follow the comments to create two dicts, or a single dictionary with tuple keys. Using tuples as keys is fine if you keep your variables inside python, but you might get into trouble when exporting to json for example.

Try a dictionary comprehension with list unpacking

names = {(name, sex): freq for name, freq, sex in data}

Or a for loop as you started

names = dict()
for name, freq, sex in data:
    names[(name, freq)] = freq

Answer 2

I'd go with something like

results = {}
for d in data:
    name, amount, gender = d.split(',')
    results[name] = data.get(name, {})
    results[name].update({ gender: amount })

this way you'll get results in smth like

{
    'Isabella': {'Girl': '42567', 'Boy': '67'}, 
    'Sophia': {'Girl': '42261'}, 
    'Jacob': {'Boy': '42164'}
}

However duplicated values will override previous, so you need to take that into account if there are some and it also assumes that the whole file matches format you've provided