CODEWITHSUNDEEP
pythondictionary
Clint Whaley
Clint Whaley

Reputation: 469

Creating a list of dictionaries in python

I have a following data set that I read in from a text file:

all_examples=   ['A,1,1', 'B,2,1', 'C,4,4', 'D,4,5']

I need to create a list of dictionary as follows:

lst = [ 
{"A":1, "B":2, "C":4, "D":4 },
{"A":1, "B":1, "C":4, "D":5 } 
]

I tried using an generator function but it was hard to create a list as such. 

attributes = 'A,B,C'
def get_examples():

    for value in examples:
        yield dict(zip(attributes, value.strip().replace(" ", "").split(',')))

Upvotes: 4

Views: 7309

Answers (4)

flaschbier
flaschbier

Reputation: 4177

Also just for fun, but with a focus on understandability:

all_examples = ['A,1,1', 'B,2,1', 'C,4,4', 'D,4,5']
ll = [ x.split(",") for x in all_examples ]
ld = list()
for col in range(1, len(ll[0])):
    ld.append({ l[0] : int(l[col]) for l in ll })
print ld

will print

[{'A': 1, 'C': 4, 'B': 2, 'D': 4}, {'A': 1, 'C': 4, 'B': 1, 'D': 5}]

Works as long as the input is csv with integers and lines are same length.

Dissection: I will use the teminology "thing" for A, B and C and "measurement" for the "columns" in the data, i.e. those values in the same "csv-column" of the inut data.

Get the string input data into a list for each line: A,1,1 -> ["A","1","1"]

ll = [ x.split(",") for x in all_examples ]

The result is supposed to be a list of dicts, so let's initialize one:

ld = list()

For each measurement (assuming that all lines have the same number of columns):

for col in range(1, len(ll[0])):

Take the thing l[0], e.g. "A", from the line and assign the numeric value int(), e.g. 1, of the measurement in the respective column l[col], e.g. "1", to the thing. Then use a dictionary comprehension to combine it into the next line of the desired result. Finally append() the dict to the result list ld. 

    ld.append({ l[0] : int(l[col]) for l in ll })

View unfoamtted. Use print json.dumps(ld, indent=4) for more convenient display:

print ld

Hope this helps. Find more on dict comprehensions e.g. here (Python3 version of this great book).

Upvotes: 3

tzaman
tzaman

Reputation: 47790

A one liner, just for fun:

all_examples = ['A,1,1', 'B,2,1', 'C,4,4', 'D,4,5']

map(dict, zip(*[[(s[0], int(x)) for x in s.split(',')[1:]] for s in all_examples]))

Produces:

[{'A': 1, 'C': 4, 'B': 2, 'D': 4}, 
 {'A': 1, 'C': 4, 'B': 1, 'D': 5}]

As a bonus, this will work for longer sequences too:

all_examples = ['A,1,1,1', 'B,2,1,2', 'C,4,4,3', 'D,4,5,6']

Output:

[{'A': 1, 'C': 4, 'B': 2, 'D': 4},
 {'A': 1, 'C': 4, 'B': 1, 'D': 5},
 {'A': 1, 'C': 3, 'B': 2, 'D': 6}]

Explanation:

map(dict, zip(*[[(s[0], int(x)) for x in s.split(',')[1:]] for s in all_examples]))
  • [... for s in all_examples] For each element in your list:
  • s.split(',')[1:] Split it by commas, then take each element after the first
  • (...) for x in and turn it into a list of tuples
  • s[0], int(x) of the first letter, with that element converted to integer
  • zip(*[...]) now transpose your lists of tuples
  • map(dict, ...) and turn each one into a dictionary!

Upvotes: 7

schafle
schafle

Reputation: 613

Your question should be "How to crate list of dictionaries?". Here's something you would like to consider.

>>> dict={}
>>> dict2={}
>>> new_list = []
>>> all_examples=['A,1,1', 'B,2,1', 'C,4,4', 'D,4,5']
>>> for k in all_examples:
...     ele=k.split(",")
...     dict[str(ele[0])]=ele[1]
...     dict[str(ele[0])]=ele[2]
...     new_list.append(dict)
...     new_list.append(dict2)
>>> dict
{'A': '1', 'C': '4', 'B': '2', 'D': '4'}
>>> dict2
{'A': '1', 'C': '4', 'B': '1', 'D': '5'}

Upvotes: 1

Alexander
Alexander

Reputation: 109546

You actually have a list of strings, and you'd like to have a list of paired dictionaries generated from the same key in the tuple triplets of each string.

To keep this relatively simple, I'll use a for loop instead of a complicated dictionary comprehension structure.

my_dictionary_list = list()
d1 = dict()
d2 = dict()
for triplet_str in all_examples:
    key, val1, val2 = triplet_str.split(',')
    d1[key] = val1
    d2[key] = val2
my_dictionary_list.append(d1)
my_dictionary_list.append(d2)

>>> my_dictionary_list
my_dictionary_list
[{'A': '1', 'B': '2', 'C': '4', 'D': '4'},
 {'A': '1', 'B': '1', 'C': '4', 'D': '5'}]

Upvotes: 1

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