Data Structure to store a Table values in python

Question

REFERENCE What can be the most efficient way to store and retrieve this type of table.

Product	Category	Original Price	Discount(%)
First	Stationary	1000	10
Second	Clothing	2000	5

stationary_items =[]
stationary_items.append({"Product" : "NOTEBOOK", "Category" : "STATIONARY", "Price" : 200, "Discount" : 20})
stationary_items.append({"Product" : "PENS", "Category" : "STATIONARY", "Price" : 300, "Discount" : 10})
stationary_items.append({"Product" : "MARKERS", "Category" : "STATIONARY", "Price" : 500, "Discount" : 5})


clothing_items = []
clothing_items.append({"Product" : "TSHIRT", "Category" : "CLOTHING", "Price" : 1000, "Discount" : 10})
clothing_items.append({"Product" : "JACKET", "Category" : "CLOTHING", "Price" : 2000, "Discount" : 5})
clothing_items.append({"Product" : "CAP", "Category" : "CLOTHING", "Price" : 500, "Discount" : 20})

I have to make queries later like if product is notebook then do something edit : I cannot use 3rd party libraries,

The code is not legal, list.append can only have one parameter at a time. BTW, you may need to use pandas. — Mechanic Pig
– Mechanic Pig, Commented Sep 10, 2022 at 8:53
A hash table (dictionary in python) is good for this kind of data. (plus you can't append more than one parameter at a time) — Chandler Bong
– Chandler Bong, Commented Sep 10, 2022 at 8:53
fixed it thankyou, but how do i make queries do you have any ideas ? — KLAUS
– KLAUS, Commented Sep 10, 2022 at 9:08

zok · Accepted Answer · 2022-09-10 10:20:16Z

1

Consider using NamedTuple since you have a fixed set of keys (table headers).

You can use one-line factory:

Point = namedtuple('Point', ['x', 'y'])

or a class-like definition with type-hints:

class Employee(NamedTuple):
    name: str
    id: int

Both of this approaches gives your a nice hints for defined attributes and allows you to not pay hashing costs.

If you have a list of such namedtuples, than you can filter it like [item for item in clothing_items if item.category == 'clothing' and product == 'tshirt'], it returns you a list of matching items.

You can describe a custom collection class, to store items hierarchically. smth like that (suppose that Product is namedtuple describing a table row):

class ProductsByCategory:
    def __init__(self):
        self._products_by_category_map: dict[str, list[Product]] = defaultdict(list)
    
    def add(product: Product):
        self._products_by_category_map[product.category].append(product)

    def __getitem__(self, category) -> [Product]:
        return self._products_by_category_map[category]

Then list of products related to 'clothing' category may be accessed like products_by_category['clothing'].

With this approach you can go further and make it "product by product name map by category map", also you can control in add method that there is only unique pairs of category and product name, so product_by_name_by_category['clothing']['tshirt'] may return you exactly one Product instance, instead of list of Product instances, so you can access it's .discount field directly.

Keep in mind possibility of KeyError while accessing products.

edited Sep 10, 2022 at 10:20

answered Sep 10, 2022 at 9:16

zok

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3 Comments

Lucas M. Uriarte Over a year ago

yes nice answer. You also have dataclasses which can be equivalent to named tuples

KLAUS Over a year ago

Thankyou for answering, but is there any way to store it like a hierarchical fashion somewhat like json, so that i can query something like if category is clothing and product is tshirt then give me the discount or price,

zok Over a year ago

I've update my answer with a pair of examples

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