What is the most efficient way to sum a dict with multiple keys by one key?

问题

I have the following dict structure.

product1 = {'product_tmpl_id': product_id,
'qty':product_uom_qty,
'price':price_unit,
'subtotal':price_subtotal,
'total':price_total,
}

And then a list of products, each item in the list is a dict with the above structure

list_ = [product1,product2,product3,.....]

I need to sum the item in the list, group by the key product_tmpl_id ... I'm using dictcollections but it only sum the qty key, I need to sum key except the product_tmpl_id which is the criteria to group by

c = defaultdict(float)
for d in list_:
    c[d['product_tmpl_id']] += d['qty']
c = [{'product_id': id, 'qty': qty} for id, qty in c.items()]

I know how to do it with a for iteration but trying to look for a more pythonic way

thanks

EDIT:

What is need is to pass from this:

lst = [
{'Name': 'A', 'qty':100,'price':10},
{'Name': 'A', 'qty':100,'price':10},
{'Name': 'A', 'qty':100,'price':10},
{'Name': 'B', 'qty':100,'price':10},
{'Name': 'C', 'qty':100,'price':10},
{'Name': 'C', 'qty':100,'price':10},
]

to this

group_lst = [
{'Name': 'A', 'qty':300,'price':30},
{'Name': 'B', 'qty':100,'price':10},
{'Name': 'C', 'qty':200,'price':20},
]

回答1:

Using basic Python, this doesn't get a whole lot better. You could hack something together with itertools.groupby, but it'd be ugly and probably slower, certainly less clear.

As @9769953 suggested, though, Pandas is a good package to handle this sort of structured, tabular data.

In [1]: import pandas as pd
In [2]: df = pd.DataFrame(lst)
Out[2]:
  Name  price  qty
0    A     10  100
1    A     10  100
2    A     10  100
3    B     10  100
4    C     10  100
5    C     10  100
In [3]: df.groupby('Name').agg(sum)
Out[3]:
      price  qty
Name
A        30  300
B        10  100
C        20  200

You just need a little extra mojo if you don't want to keep the data as a dataframe:

In [4]: grouped = df.groupby('Name', as_index=False).agg(sum)
In [5]: list(grouped.T.to_dict().values())
Out[5]:
[{'Name': 'A', 'price': 30, 'qty': 300},
 {'Name': 'B', 'price': 10, 'qty': 100},
 {'Name': 'C', 'price': 20, 'qty': 200}]

回答2:

On the verbose side, but gets the job done:

group_lst = []
lst_of_names = []
for item in lst:
    qty_total = 0
    price_total = 0

    # Get names that have already been totalled
    lst_of_names = [item_get_name['Name'] for item_get_name in group_lst]

    if item['Name'] in lst_of_names:
        continue

    for item2 in lst:
        if item['Name'] == item2['Name']:
            qty_total += item2['qty']
            price_total += item2['price']

    group_lst.append(
        {
            'Name':item['Name'],
            'qty':qty_total,
            'price':price_total
        }
    )
pprint(group_lst)

Output:

[{'Name': 'A', 'price': 30, 'qty': 300},
 {'Name': 'B', 'price': 10, 'qty': 100},
 {'Name': 'C', 'price': 20, 'qty': 200}]

回答3:

You can use defaultdict and Counter

>>> from collections import Counter, defaultdict
>>> cntr = defaultdict(Counter)
>>> for d in lst:
...     cntr[d['Name']].update(d)
...
>>> res = [dict(v, **{'Name':k}) for k,v in cntr.items()]
>>> pprint(res)
[{'Name': 'A', 'price': 30, 'qty': 300},
 {'Name': 'C', 'price': 20, 'qty': 200},
 {'Name': 'B', 'price': 10, 'qty': 100}]

来源：https://stackoverflow.com/questions/50974070/what-is-the-most-efficient-way-to-sum-a-dict-with-multiple-keys-by-one-key

标签

python

python-2.7

python-collections