CODEWITHSUNDEEP
pythonlistset
oz123
oz123

Reputation: 28878

Make sets from a list of lists in Python

I have a list of lists in the form:

testdata = [['9034968', 'ETH'],  ['14160113', 'ETH'],  ['9034968', 'ETH'],  
            ['11111', 'NOT'], ['9555269', 'NOT'],  ['15724032', 'ETH'],  
            ['15481740', 'ETH'],  ['15481757', 'ETH'],  ['15481724', 'ETH'],   
            ['10307528', 'ETH'],  ['15481757', 'ETH'],  ['15481724', 'ETH'],
            ['15481740', 'ETH'],  ['15379365', 'ETH'],  ['11111', 'NOT'],
            ['9555269', 'NOT'],  ['15379365', 'ETH']]

I would like to have a final result which groups the unique name with their values. So in the finall list (or dictinary, or any iterable) there are only two names (ETH and NOT) with a list as the second item of all the other values, e.g:

In [252]: unique_names
Out[252]: 
{'ETH': ['9034968',
  '14160113',
  '9034968',
  '15724032',
  '15481740',
  '15481757',
  '15481724',
  '10307528',
  '15481757',
  '15481724',
  '15481740',
  '15379365',
  '15379365'],
 'NOT': ['11111', '9555269', '11111', '9555269']}

To achieve this I used a dictionary and the following steps:

unique_names = []

for (x,y) in testdata: 
    if y not in unique_names:
       unique_names.append(y)

# now unique_names is ['ETH', 'NOT']

unique_names = {name:list() for name in unique_names}

for (x,y) in testdata: unique_names[y]=unique_names[y]+[x]

#so finally I get the result above

My problem is:

The example data for this question was take from a similar question about sets and list here: Python: Uniqueness for list of lists. Unfortunately, the OP there wanted a different result, but the structure of data was appropriate enough.

Upvotes: 0

Views: 216

Answers (1)

thefourtheye
thefourtheye

Reputation: 239653

You can use defaultdict like this

from collections import defaultdict
d = defaultdict(list)

for (value, key) in testdata:
    d[key].append(value)

print d

Or with a normal dictionary

d = {}
for (value, key) in testdata:
    d.setdefault(key, []).append(value)
print d

Both the examples are based on the same idea. They group the values as a list based on the key. The dict.setdefault will assign the default value to the key, if the key is not present in the dictionary already, and then the value will be returned. We just keep appending the values to the list corresponding to the key.

Upvotes: 3

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