Group a multidimensional array by a key in python

Question

I have this code :

 [
    {
        "info": {
            "a": 65535,
            "b": 50,
        },
        "test": {
            "m": "10300",
            "id": "2008",
        },
    },
    {
        "info": {
            "a": 65535,
            "b": 50,
        },
        "test": {
            "m": "10300",
            "id": "2008",
        },
    },
    {
        "info": {
            "a": 65535,
            "b": 50,
        },
        "test": {
            "m": "10300",
            "id": "2009",
        },
    },
]

I want to have :

[
    "2008" : [
        {
            "info": {
                "a": 65535,
                "b": 50,
             },
            "test": {
                "m": "10300",
                "id": "2008",
             },
        },
        {
            "info": {
                "a": 65535,
                "b": 50,
            },
            "test": {
                "m": "10300",
                "id": "2008",
            },
       },
    ]
    "2009" : [
        {
            "info": {
                "a": 65535,
                "b": 50,
            },
            "test": {
                "m": "10300",
                "id": "2009",
            },
        },
     ]

The idea is to group by key value based on column id. I'm new in python an have no idea how to do that. Please help me. Thx in advance. If you could provide some ideas will be great.I found some examples but can't solve this problem anyway.

My solution :

value = [i for i in array]
res = sorted(value, key=lambda x: x["id"], reverse=True)

Please show what you've tried...

l'L'l
– l'L'l

2018-08-14 08:29:01 +00:00
Commented Aug 14, 2018 at 8:29 — l'L'l
– l'L'l, Commented Aug 14, 2018 at 8:29
@I'L'I I edited the question

GPiter
– GPiter

2018-08-14 08:31:25 +00:00
Commented Aug 14, 2018 at 8:31 — GPiter
– GPiter, Commented Aug 14, 2018 at 8:31
Your desired output is a syntax error.

Aran-Fey
– Aran-Fey

2018-08-14 08:31:47 +00:00
Commented Aug 14, 2018 at 8:31 — Aran-Fey
– Aran-Fey, Commented Aug 14, 2018 at 8:31

Ozzy Walsh · Accepted Answer · 2018-08-14 08:41:30Z

3

I think you want a dictionary where each key is the id and the value is your object.

Try the following. data is your array of data.

new = {}
for item in data:
    item_id = item['test']['id']
    new[item_id] = item

You could also use a dictionary comprehension.

new = {item['test']['id']: item for item in data}

edited Aug 14, 2018 at 8:41

answered Aug 14, 2018 at 8:33

Ozzy Walsh

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6 Comments

GPiter Over a year ago

Is getting only the first value

GPiter Over a year ago

can you take a look please ?

Ozzy Walsh Over a year ago

@George what do you mean?

GPiter Over a year ago

I get : for each id only one item, for example : ` "2008" : [ { "info": { "a": 65535, "b": 50, }, "test": { "m": "10300", "id": "2008", }, },]`

GPiter Over a year ago

But I have 2 items for key 2008

|

Sunitha · Accepted Answer · 2018-08-14 08:38:43Z

1

Use itertools.groupby

from itertools import groupby
f = lambda d: d['test']['id']
res = {k:list(v) for k,v in groupby(sorted(l, key=f), f)}
pprint(res)

Output

{'2008': [{'info': {'a': 65535, 'b': 50},
           'test': {'id': '2008', 'm': '10300'}},
          {'info': {'a': 65535, 'b': 50},
           'test': {'id': '2008', 'm': '10300'}}],
 '2009': [{'info': {'a': 65535, 'b': 50},
           'test': {'id': '2009', 'm': '10300'}}]}

answered Aug 14, 2018 at 8:38

Sunitha

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Comments

KBA7 · Accepted Answer · 2018-08-14 10:28:36Z

Let us suppose

array = [
   {
    "info": {
        "a": 65535,
        "b": 50,
        },
    "test": {
        "m": "10300",
        "id": "2008",
        },
    },
    {
    "info": {
        "a": 65535,
        "b": 50,
        },
    "test": {
        "m": "10300",
        "id": "2008",
        },
    },
    {
    "info": {
        "a": 65535,
        "b": 50,
        },
    "test": {
        "m": "10300",
        "id": "2009",
        },
    },
]

Then you can get the expected result by using

modified_data = {}
for entry in array:
    index = entry['test']['id']
    try:
        modified_data[index].append(entry)
    except KeyError:
        modified_data[index] = [entry]
print modified_data

Now let's analyze your code

value = [i for i in array]

After this value will be equal to array itself, assuming that your array initialization is same as mine.

res = sorted(value, key=lambda x: x["id"], reverse=True)

If the above statement is correct then value will not have 'id' hence it will throw an error.

Also, a list can't have a key-value pair. You have to use a dictionary for that.

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