CODEWITHSUNDEEP
pythonlistdictionary
Tim
Tim

Reputation: 99428

A dict and a list of dicts: conversion and when to use which

  1. How can we convert a dict with tuples (key, value), into a list of dicts, each dict with keys "key" and "value"?

    For example:

    dic={'Tim':3, 'Kate':2}

    becomes

    lst = [{'Name':'Tim', 'Age':3}, {'Name':'Kate', 'Age':2}]
  2. What are some advantages and disadvantages of using each representation? (e.g. consider the operations which we can think of and apply to them naturally). Thanks.

Upvotes: 1

Views: 659

Answers (3)

Vivek Sable
Vivek Sable

Reputation: 10223

Dictionary to list of dictionary 

>>> dic={'Tim':3, 'Kate':2}
>>> [{"Name":i, "Age":j} for i,j in dic.items()]
[{'Age': 3, 'Name': 'Tim'}, {'Age': 2, 'Name': 'Kate'}]
>>>

Best to use Dictionary Data Structure because Time Complexity to Find Key is O(1) Constant Time i.e. it is not depend on the size of dictionary

Demo to find age of Kate.

Need to Iterate every element from the List. Time Complexity is from O(1) to O(N)

>>> info
[{'Age': 3, 'Name': 'Tim'}, {'Age': 2, 'Name': 'Kate'}]
>>> age = -1
>>> find_name = "Kate"
>>> for i in info:
...    if i["Name"]==find_name:
...      age = i["Age"]
...      break
... 
>>> age
2
>>>

By dictionary: Time Complexity is O(1)

>>> dic = {'Tim':3, 'Kate':2}
>>> find_name = "Kate"
>>> if find_name in dic:
...    age = dic[find_name]
... else:
...    age = -1
...    print "No data for %s name"%find_name
... 
>>> age
2
>>>

Upvotes: 4

Kasravnd
Kasravnd

Reputation: 107297

You can use a list comprehension :

>>> dic={'Tim':3, 'Kate':2}
>>> [{'Name':i, 'Age':j} for i,j in dic.items()]
[{'Age': 3, 'Name': 'Tim'}, {'Age': 2, 'Name': 'Kate'}]

and for opposite :

>>> l=[{'Name':i, 'Age':j} for i,j in dic.items()]
>>> dict((i.values()[::-1] for i in l))
{'Tim': 3, 'Kate': 2}

Upvotes: 5

Bhargav Rao
Bhargav Rao

Reputation: 52101

Another way using map

>>> dic={'Tim':3, 'Kate':2}
>>> map(lambda x: x,dic)
['Tim', 'Kate']
>>> map(lambda x:{'Age':dic[x],'Name':x},dic)
[{'Age': 3, 'Name': 'Tim'}, {'Age': 2, 'Name': 'Kate'}]
>>>

Note - map is slower compared to a list comprehension, but I have just added it as an alternative

Upvotes: 3

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