How can I get the keys from a nested dictionary?

Question

I have a list within a dictionary within a dictionary:

{FirmA:{ProductA:[Color1,Color2,Color3]}}

I want to build a list of keys from the First Firm dictionary level.

Then, I need to access the second level Product dictionary based on a Firm Key.

Finally, I will need to access the Colors list based on the Product key from Dictionary level 2 (Products).

I tried to get the level 1 keys for Firms:

[i for i in dict.keys()]

Returns

ValueError: Too many values to unpack

This is a fairly large data set.

I have not been able to get to the 2nd level dictionary yet.

@shash678 I updated it in my answer, the actual dictionary I am using is too large. — Alex, Jul 25 '19 at 23:46
If you still need help, please provide a [mcve] that causes the error you are asking about. — Code-Apprentice, Oct 02 '19 at 19:28

score 0 · Answer 1 · edited Oct 02 '19 at 19:26

0

What about that:

d = {'foo':{'bar':42}}

# you can do much like for nested list, like so:
print(d['foo'])
print(d['foo']['bar'])

# or you can iterate:
for k,v in d.items():
    print(k,v)

    # if the value is also a dictionary, iterate on it again:
    try:
        for k2, v2 in v.items():
            if isinstance(v2, list):
                for el in v2:
                    print el
    except:
        pass

EDIT: actually if it's a large dataset, and you'll have few values below the first pass actually a dictionary, it may be faster to do an instance check as well (isinstance(v, dict)), since catching is expensive. Depends on the details....

edited Oct 02 '19 at 19:26

marc_s

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answered Jul 25 '19 at 23:44

logicOnAbstractions

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```for k,v in d.items(): print(k,v)``` this works to print, but I need to append these keys to a list. Then, the next step will be to access the 2nd dictionary using keys from the first dictionary list. – Alex Jul 25 '19 at 23:51
Just so it's easy to copy-past the whole thing to see/understand the output. Then you do whatever you need with it! – logicOnAbstractions Jul 25 '19 at 23:51
```for key, value in d.iteritems(): li.append(key)``` Returns ```ValueError: Too many values to unpack``` Note: I am on Python 2.7 – Alex Jul 25 '19 at 23:55
It's actually not so clear what you want to do with what. Above you have the syntax you can use to manipulate the dictionnary... either clarify the question or use the above. You do have the tools you need with that to access whatever is needed in your data. – logicOnAbstractions Jul 25 '19 at 23:57
[Cathing is expensive](https://stackoverflow.com/a/2522013/307138)? It might be, depending on the data structure, but that is up to the OP to do some tests ;) – Ocaso Protal Jul 26 '19 at 07:12

score 0 · Answer 2 · answered Jul 26 '19 at 00:02

Something like this should get you started:

def get_products_for_firm(d, firm):
    firm_letter = firm[-1]
    product_prefix = "Product"
    product_key = "%s%s" % (product_prefix, firm_letter)
    return d[firm][product_key]


d = {
    "FirmA": {
        "ProductA": ["Color1", "Color2", "Color3"]
    },
    "FirmB": {
        "ProductB": ["Color4", "Color5", "Color6"]
    }
}

firm_keys = d.keys()
print "The firm keys are %s: " % (firm_keys)

for firm_key in firm_keys:
    print "The products for %s are: %s" % (firm_key,
                                           get_products_for_firm(d, firm_key))

Output:

The firm keys are ['FirmA', 'FirmB']:
The products for FirmA are: ['Color1', 'Color2', 'Color3']
The products for FirmB are: ['Color4', 'Color5', 'Color6']

edd313 · Answer 3 · 2023-01-03T17:37:22.820

With a NestedDict you can extract keys of a nested dictionary as it was flat.

from ndicts import NestedDict

d = {"FirmA": {"ProductA": ["red", "blue", "yellow"],
               "ProductB": ["grey", "white"]},
     "FirmB": {"ProductB": ["black"]}}
nd = NestedDict(d)

>>> keys = list(nd.keys())
>>> keys
[('FirmA', 'ProductA'), ('FirmA', 'ProductB'), ('FirmB', 'ProductB')]

If you want to access a specific level use a comprehension

>>> 1st_level = [key[0] for key in keys]
>>> 2nd_level = [key[1] for key in keys]
>>> 1st_level, 2nd_level
(['FirmA', 'FirmA', 'FirmB'], ['ProductA', 'ProductB', 'ProductB'])

If you need to access an item:

>>> nd["FirmA", "ProductB"]
['grey', 'white']

To install ndicts pip install ndicts.

Finally, you said that you have a large dataset. While a NestedDict will give you what you want, it is not meant to be performing fast. It is simply meant to give you a simple interface to work with on nested dictionaries. Check out pandas Dataframes to speed up lookups. In particular have a look at MultiIndex, which are great to store hyerarchical data like yours.

How can I get the keys from a nested dictionary?

3 Answers3

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