CODEWITHSUNDEEP
pythondictionary
Ali
Ali

Reputation: 67

How to read files with one key but multiple values in Python

I am just beginning working with Python and am a little confused. I understand the basic idea of a dictionary as (key, value). I am writing a program and want to read in a file, story it in a dictionary and then complete different functions by referrencing the values. I am not sure if I should use a dictionary or lists. The basic layout of the file is: Name followed by 12 different years for example : A 12 12 01 11 0 0 2 3 4 9 12 9

I am not sure what the best way to read in this information would be. I was thinking that a dictionary may be helpful if I had Name followed by Years, but I am not sure if I can map 12 years to one key name. I am really confused on how to do this. I can read in the file line by line, but not within the dictionary. 

def readInFile():
    fileDict ={"Name ": "Years"}
    with open("names.txt", "r") as f:
        _ = next(f)
        for line in f:
                if line[1] in fileDict:
                    fileDict[line[0]].append(line[1])
                else:
                    fileDict[line[0]] = [line[1]]

My thinking with this code was to append each year to the value. Please let me know if you have any recommendations.

Thank you!

Upvotes: 0

Views: 2240

Answers (3)

BoarGules
BoarGules

Reputation: 16942

You can map 12 years to one key name. You seem to think that you need to choose between a dictionary and a list ("I am not sure if I should use a dictionary or lists.") But those are not alternatives. Your 12 years can usefully be represented as a list. Your names can be dictionary keys. So you need (as PM 2Ring suggests) a dictionary where the key is a name and the value is a list of years.

def readInFile():
    fileDict = {}
    with open(r"names.txt", "r") as f:
        for line in f:
            name, years = line.split(" ",1)
            fileDict[name] = years.split()

There are two calls to the string method split(). The first splits the name from the years at the first space. (You can get the name using line[0], but only if the name is one character long, and that is unlikely to be useful with real data.) The second call to split() picks the years apart and puts them in a list.

The result from the one-line sample file will be the same as running this: 

fileDict = {'A': ['12', '12', '01', '11', '0', '0', '2', '3', '4', '9', '12', '9']}

As you can see, these years are strings not integers: you may want to convert them.

Rather than doing:

_ = next(f)

to throw away your record count, consider doing

for line in f:
    if line.strip().isdigit():
        continue

instead. If you are using file's built-in iteration (for line in f) then it's generally best not to call next() on f yourself.

It's also not clear to me why your code is doing this:

fileDict ={"Name ": "Years"}

This is a description of what you plan to put in the dictionary, but that is not how dictionaries work. They are not database tables with named columns. If you use a dictionary with key:name and value:list of years, that structure is implicit. The best you can do is describe it in a comment or a type annotation. Performing the assignment will result in this:

fileDict = {
           'A': ['12', '12', '01', '11', '0', '0', '2', '3', '4', '9', '12', '9'],
           'Name ': 'Years'
           }

which mixes up description and data, and is probably not what you want, because your subsequent code is likely to expect a 12-list of years in the dictionary value, and if so it will choke on the string "Years".

Upvotes: 0

Aaditya Ura
Aaditya Ura

Reputation: 12669

You can do in one line :)

print({line[0]:line[1:].split() for line in open('file.txt','r') if line[0]!='\n'})

output:

{'A': ['12', '12', '01', '11', '0', '0', '2', '3', '4', '9', '12', '9']}

Above dict comprehension is same as:

dict_1={}
for line in open('legend.txt', 'r'):
    if line[0]!='\n':
        dict_1[line[0]]=line[1:].split()

print(dict_1)

Upvotes: 1

ahed87
ahed87

Reputation: 1360

Values in a dict can be anything, including a new dict, but in this case a list sounds good. Maybe something like this.

from io import StringIO # just to make it run without an actual file

the_file_content = 'A 12 12 01 11\nB 13 13 02'
fake_file = StringIO(the_file_content)

# this stays for your
#with open('names.txt', 'rt') as f:
#    lines = f.readlines()

lines = fake_file.readlines() # this goes away for you

lines = [l.strip().split(' ') for l in lines]

fileDict = {row[0]: row[1:] for row in lines}

# if you want the values to be actual numbers rather than strings
for k, v in fileDict.items():
    fileDict[k] = [int(i) for i in v]

In python there are constructs where most simple as well as complex things can be done in one go, rather than looping with index-like constructs.

Upvotes: 0

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