CODEWITHSUNDEEP
pythondictionaryordereddict
Eka
Eka

Reputation: 15002

How to create an OrderedDict in Python?

I tried to maintain the order of a Python dictionary, since native dict doesn't have any order to it. Many answers in SE suggested using OrderedDict.

from collections import OrderedDict

domain1 = { "de": "Germany", "sk": "Slovakia", "hu": "Hungary",
    "us": "United States", "no": "Norway"  }

domain2 = OrderedDict({ "de": "Germany", "sk": "Slovakia", "hu": "Hungary",
    "us": "United States", "no": "Norway"  })

print domain1
print " "    
for key,value in domain1.iteritems():
    print (key,value)

print " "

print domain2
print ""
for key,value in domain2.iteritems():
    print (key,value)

After iteration, I need the dictionary to maintain its original order and print the key and values as original:

{
    "de": "Germany",
    "sk": "Slovakia",
    "hu": "Hungary",
    "us": "United States",
    "no": "Norway"
}

Either way I used doesn't preserve this order, though.

Upvotes: 49

Views: 58180

Answers (5)

alex
alex

Reputation: 7471

In Python 3.7+, dictionaries are ordered by-default. The documentation says that "the insertion-order preservation nature of dict objects have been declared to be an official part of the Python language spec".

The following code will print each item in the same order in which it was inserted, without the use of an OrderedDict class:

dictionary = dict()

dictionary["de"] = "Germany"
dictionary["sk"] = "Slovakia"
dictionary["hu"] = "Hungary"
dictionary["us"] = "United States"
dictionary["no"] = "Norway"

for key, value in dictionary.items():
    print(key, value)
 
>>   de Germany
>>   sk Slovakia
>>   hu Hungary
>>   us United States
>>   no Norway

Upvotes: 0

Mark
Mark

Reputation: 92461

You need to pass it a sequence of items or insert items in order - that's how it knows the order. Try something like this:

from collections import OrderedDict

domain = OrderedDict([('de', 'Germany'),
                      ('sk', 'Slovakia'),
                      ('hu', 'Hungary'),
                      ('us', 'United States'),
                      ('no', 'Norway')])

The array has an order, so the OrderedDict will know the order you intend.

Upvotes: 76

Pedro Lobito
Pedro Lobito

Reputation: 99031

Late answer, but here's a python 3.6+ oneliner to sort dictionaries by key without using imports:

d = { "de": "Germany", "sk": "Slovakia", "hu": "Hungary",
    "us": "United States", "no": "Norway"  }
d_sorted = {k: v for k, v in sorted(d.items(), key=lambda x: x[1])}
print(d_sorted)

Output:

{'de': 'Germany', 'hu': 'Hungary', 'no': 'Norway', 'sk': 'Slovakia', 'us': 'United States'}

Python Demo

Upvotes: 3

Fabien
Fabien

Reputation: 4972

You can use OrderedDict but you have to take in consideration that OrderedDict will not work outside of your running code.

This means that exporting the object to JSON will lose all the effects of OrderedDict.

What you can do is create a metadata array in which you can store the keys "de", sk", etc. in an ordered fashion. By browsing the array in order you can refer to the dictionary properly, and the order in array will survive any export in JSON, YAML, etc.

Current JSON:

{ "de": "Germany", "sk": "Slovakia", "hu": "Hungary", "us": "United States", "no": "Norway"  }

New object countries:

countries = {
  "names" : { 
    "de": "Germany", "sk": "Slovakia", "hu": "Hungary", "us": "United States", "no": "Norway"  
  },
  "order" : [ 
    "de", "sk", "hu", "us", "no" 
  ]
}

Code that will print the long names in order:

for code in countries['order']:
 print(countries['names'][code])

Upvotes: 2

Jared Goguen
Jared Goguen

Reputation: 9008

In the OrderedDict case, you are creating an intermediate, regular (and hence unordered) dictionary before it gets passed to the constructor. In order to keep the order, you will either have to pass something with order to the constructor (e.g. a list of tuples) or add the keys one-by-one in the order you want (perhaps in a loop).

Upvotes: 4

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