从一个字典中提取多个键：值对到一个新的字典

Question

I have a list of dict what some data, and I would like to extract certain key:value pairs into a new list of dicts. I know one way that I could do this would be to use del i['unwantedKey'] , however, I would rather not delete any data but instead create a new dict with the needed data.

The column order might change, so I need something to extract the two key:value pairs from the larger dict into a new dict.

Current Data Format

[{'Speciality': 'Math', 'Name': 'Matt', 'Location': 'Miami'},
 {'Speciality': 'Science', 'Name': 'Ben', 'Location': 'Las Vegas'}, 
 {'Speciality': 'Language Arts', 'Name': 'Sarah', 'Location': 'Washington DC'},
 {'Speciality': 'Spanish', 'Name': 'Tom', 'Location': 'Denver'},
 {'Speciality': 'Chemistry', 'Name': 'Jim', 'Location': 'Dallas'}]

Code to delete key:value from dict

import csv

data= []
for line in csv.DictReader(open('data.csv')):
    data.append(line)

for i in data:
    del i['Speciality']

print data

Desired Data Format without using del i['Speciality']

[{'Name': 'Matt', 'Location': 'Miami'}, 
 {'Name': 'Ben', 'Location': 'Las Vegas'}, 
 {'Name': 'Sarah', 'Location': 'Washington DC'}, 
 {'Name': 'Tom', 'Location': 'Denver'}, 
 {'Name': 'Jim', 'Location': 'Dallas'}]

Answer 1

If you want to give a positive list of keys to copy over into the new dictionaries:

import csv

with open('data.csv', 'rb') as csv_file:
    data = list(csv.DictReader(csv_file))

keys = ['Name', 'Location']
new_data = [dict((k, d[k]) for k in keys) for d in data]

print new_data

Answer 2

suppose we have,

l1 = [{'Location': 'Miami', 'Name': 'Matt', 'Speciality': 'Math'},
      {'Location': 'Las Vegas', 'Name': 'Ben', 'Speciality': 'Science'},
      {'Location': 'Washington DC', 'Name': 'Sarah', 'Speciality': 'Language Arts'},
      {'Location': 'Denver', 'Name': 'Tom', 'Speciality': 'Spanish'},
      {'Location': 'Dallas', 'Name': 'Jim', 'Speciality': 'Chemistry'}]

to create a new list of dictionaries that do not contain the keys 'Speciality' we can do,

l2 = []
for oldd in l1:
    newd = {}
    for k,v in oldd.items():
        if k != 'Speciality':
            newd[k] = v
    l2.append(newd)

and now l2 will be your desired output. In general you can exclude an arbitrary list of keys like so

exclude_keys = ['Speciality', 'Name']
l2 = []
    for oldd in l1:
        newd = {}
        for k,v in oldd.items():
            if k not in exclude_keys:
                newd[k] = v
        l2.append(newd)

the same can be done with an include_keys variable

include_keys = ['Name', 'Location']
l2 = []
    for oldd in l1:
        newd = {}
        for k,v in oldd.items():
            if k in include_keys:
                newd[k] = v
        l2.append(newd)

Answer 3

You can create a new list of dicts limited to the keys you want with one line of code (Python 2.6+):

NLoD=[{k:d[k] for k in ('Name', 'Location')} for d in LoD]

Try it:

>>> LoD=[{'Speciality': 'Math', 'Name': 'Matt', 'Location': 'Miami'},
 {'Speciality': 'Science', 'Name': 'Ben', 'Location': 'Las Vegas'}, 
 {'Speciality': 'Language Arts', 'Name': 'Sarah', 'Location': 'Washington DC'},
 {'Speciality': 'Spanish', 'Name': 'Tom', 'Location': 'Denver'},
 {'Speciality': 'Chemistry', 'Name': 'Jim', 'Location': 'Dallas'}]
>>> [{k:d[k] for k in ('Name', 'Location')} for d in LoD]
[{'Name': 'Matt', 'Location': 'Miami'}, {'Name': 'Ben', 'Location': 'Las Vegas'}, {'Name': 'Sarah', 'Location': 'Washington DC'}, {'Name': 'Tom', 'Location': 'Denver'}, {'Name': 'Jim', 'Location': 'Dallas'}]

Since you are using csv, you can limit the columns that you read in the first place to the desired columns so you do not need to delete the undesired data:

dc=('Name', 'Location')        
with open(fn) as f:
    reader=csv.DictReader(f)
    LoD=[{k:row[k] for k in dc} for row in reader]

Answer 4

keys_lst = [Name', 'Location]

new_data={key:val for key,val in event.items() if key in keys_lst}
print(new_data)