Sort a JSON using Python

Question

I am trying ot sort a JSON Object using Python.

I have the following object :

{ 
  "text": "hello world",
  "predictions": 
   [
     {"class": "Class 1", "percentage": 4.63},
     {"class": "Class 2", "percentage": 74.68},
     {"class": "Class 3", "percentage": 9.38},
     {"class": "Class 4", "percentage": 5.78},
     {"class": "Class 5", "percentage": 5.53}
   ]
}

And I want to have this object instead :

{ 
  "text": "hello world",
  "predictions": 
   [
     {"class": "Class 2", "percentage": 74.68},
     {"class": "Class 3", "percentage": 9.38},
     {"class": "Class 4", "percentage": 5.78},
     {"class": "Class 5", "percentage": 5.53},
     {"class": "Class 1", "percentage": 4.63}
   ]
}

In fact, I want to order my array of objects by percentage.

I have tried this command :

sorted_obj = sorted(json_obj['predictions'], key=lambda k: k['percentage'], reverse=True)

And I had this error :

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: string indices must be integers

Any help is needed,

Thanks

JSON arrays are parsed to Python lists and JSON objects to Python dicts. dicts are unordered in Python. You would need some ordered container. Try to store the data in an OrderedDict: from collections import OrderedDict — Adirio
– Adirio, Commented Apr 6, 2017 at 13:00
I trust you realise "nothing worked" is an unhelpful description of your problem. It implies it's the reader's duty to determine the exact nature of the problem. Most people will walk away, others like me will add a comment intended to be helpful, but very few will attempt to answer such an ill-defined question. Give yourself a chance to get help, tell us what's wrong! — holdenweb
– holdenweb, Commented Apr 6, 2017 at 13:01
@Adirio - he isn't trying to order a dict, he's trying to order a list of dicts based on one of the values in the dicts. — holdenweb
– holdenweb, Commented Apr 6, 2017 at 13:02
@Adirio yeah, made similar mistakes myself a million times, no sweat. — holdenweb
– holdenweb, Commented Apr 6, 2017 at 16:26

Satish Prakash Garg · Accepted Answer · 2017-04-06 13:18:42Z

16

You can use sorted to sort the values, something like this :

json_obj = { 
  "text": "hello world",
  "predictions": 
   [
     {"class": "Class 1", "percentage": 4.63},
     {"class": "Class 2", "percentage": 74.68},
     {"class": "Class 3", "percentage": 9.38},
     {"class": "Class 4", "percentage": 5.78},
     {"class": "Class 5", "percentage": 5.53}
   ]
}

sorted_obj = dict(json_obj) 
sorted_obj['predictions'] = sorted(json_obj['predictions'], key=lambda x : x['percentage'], reverse=True)

print(sorted_obj)
print(json_obj)

This will result in :

# The sorted values based on 'predictions' -> 'percentage'
{'predictions': [{'percentage': 74.68, 'class': 'Class 2'}, {'percentage': 9.38, 'class': 'Class 3'}, {'percentage': 5.78, 'class': 'Class 4'}, {'percentage': 5.53, 'class': 'Class 5'}, {'percentage': 4.63, 'class': 'Class 1'}], 'text': 'hello world'}

# The original json_obj will remain unchanged as we have created a new object sorted_obj from values of json_obj using dict()
{'text': 'hello world', 'predictions': [{'class': 'Class 1', 'percentage': 4.63}, {'class': 'Class 2', 'percentage': 74.68}, {'class': 'Class 3', 'percentage': 9.38}, {'class': 'Class 4', 'percentage': 5.78}, {'class': 'Class 5', 'percentage': 5.53}]}

edited Apr 6, 2017 at 13:18

answered Apr 6, 2017 at 13:11

Satish Prakash Garg

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4 Comments

shad0w_wa1k3r Over a year ago

Note that this is an in-place edit of the original json. It will overwrite it.

Satish Prakash Garg Over a year ago

@AshishNitinPatil No, it wont. I am creating new object using the old values and not creating a direct reference.

shad0w_wa1k3r Over a year ago

My bad, I thought replacing list in a key should change the original as well.

Harshit verma Over a year ago

Why have you done this? sorted_obj = dict(json_obj) , whats its significance?

shad0w_wa1k3r · Accepted Answer · 2017-04-06 13:35:27Z

2

You are almost right, you probably want to create a copy of the dictionary and then replace predictions's value to the sorted object. I'm assuming that you want to leave the original json_obj unchanged, hence the deepcopy (although it is unnecessary if we are simply doing a reassignment instead of in-place .sort).

>>> json_obj = { 
...   "text": "hello world",
...   "predictions": 
...    [
...      {"class": "Class 1", "percentage": 4.63},
...      {"class": "Class 2", "percentage": 74.68},
...      {"class": "Class 3", "percentage": 9.38},
...      {"class": "Class 4", "percentage": 5.78},
...      {"class": "Class 5", "percentage": 5.53}
...    ]
... }
>>> from copy import deepcopy
>>> sorted_json_obj = deepcopy(json_obj)
>>> sorted_json_obj['predictions'] = sorted(json_obj['predictions'], key=lambda k: k['percentage'], reverse=True)
>>> sorted_json_obj
{'predictions': [{'class': 'Class 2', 'percentage': 74.68},
                 {'class': 'Class 3', 'percentage': 9.38},
                 {'class': 'Class 4', 'percentage': 5.78},
                 {'class': 'Class 5', 'percentage': 5.53},
                 {'class': 'Class 1', 'percentage': 4.63}],
 'text': 'hello world'}

edited Apr 6, 2017 at 13:35

answered Apr 6, 2017 at 13:02

shad0w_wa1k3r

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3 Comments

ben Over a year ago

My bad, my object wasn't well parsed. Thanks for your time :)

Satish Prakash Garg Over a year ago

@ben @Ashish Note : For simple data structures, using deepcopy can be an overkill, since it does so much accounting, reference tracking, and the like. Look at this : writeonly.wordpress.com/2009/05/07/…

shad0w_wa1k3r Over a year ago

Yep, reassignment would be okay here, but in-place sorting won't be. Had a great discussion in chat about it. Thanks @SatishGarg!

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