CODEWITHSUNDEEP
pythondictionary
user1063450
user1063450

Reputation:

In Python, how do you edit the values in a dictionary based on the frequency of its key?

I'm creating a program that reads through a .txt file of names (lastname,firstname), one per line, and creates a dictionary that shows the number of times a specific first name repeats.

I've gotten the follow code so far but can't seem to accurately count the number of times a first name repeats. I think the problem is that my variable "value" doesn't correspond to the actual value in the key value pair. How can I fix that?

file = open('names.txt')

dict = {}
value = 1

for line in file:
    listOfNames = line.split(",")
    firstName = listOfNames[1]

    if dict.has_key(firstName):
        value += 1
    else: 
        dict[firstName] = value

file.close()

Upvotes: 4

Views: 295

Answers (6)

ninjagecko
ninjagecko

Reputation: 91132

with open('names.txt') as f:
    firstNames = [line.split(',')[0] for line in f]

print collections.Counter(firstNames)

Upvotes: 2

sholsapp
sholsapp

Reputation: 16080

Use a defaultdict like this:

from collections import defaultdict
d = defaultdict(int)
for name in open('names.txt'):
  _, first_name = name.split(",")
  d[first_name] += 1

You may want to normalize your names by stripping whitespace and capitalization.

Upvotes: 2

Praveen Gollakota
Praveen Gollakota

Reputation: 38980

As @Aurora mentions, Counter is perfect for this.

>>> names = ['foo bar', 'foo baz', 'foo car', 'doo bar', 'doo baz', 'boo paz']
>>> from collections import Counter
>>> Counter(name.split()[1] for name in names)
Counter({'baz': 2, 'bar': 2, 'paz': 1, 'car': 1})

Upvotes: 2

Raymond Hettinger
Raymond Hettinger

Reputation: 226564

You can replace the if-block with:

dict[firstname] = dict.get(firstname, 0) + 1

Alternatively, you can use collections.Counter instead of a dict. That simplifies to counting code to just:

c[firstname] += 1

where c is a Counter instance.

Upvotes: 2

Aurora
Aurora

Reputation: 4414

You may be interested in the collections.Counter - which is a special dictionary for exactly this kind of task.

Upvotes: 6

Greg Hewgill
Greg Hewgill

Reputation: 994101

It looks like you want something like:

if dict.has_key(firstName):
    dict[firstName] += 1
else:
    dict[firstName] = 1

Also, I would strongly recommend you choose a name other than dict, such as names. The reason is that dict is the name of the standard Python dictionary type (just like you usually don't want to create Python variables called str, int, or list).

There are other solutions such as using collections.defaultdict that will be more succinct.

Upvotes: 2

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