CODEWITHSUNDEEP
pythonpython-3.x
Colin
Colin

Reputation: 670

Reduce list to a dictionary of lists

I'm pulling a bunch of rows out of my database, many of which share a similar ID. I want to group the ones with the same ID into a list and generate a map that maps from the ID to the list of results. I have the following code, but it seems like there must be a simpler way of doing it with reduce or dictionary comprehension:

result = {}
for row in rows:
  type_id = row['type_id']
  values = result.get(type_id, [])
  values.append(row)
  result[type_id] = values

Upvotes: 0

Views: 161

Answers (2)

Volodymyr Boyko
Volodymyr Boyko

Reputation: 1581

btw if you are asking for oneliner comprehension. Not sure about "simplier" part though =)

{type_id:[row for row in rows if row["type_id"] == type_id] for type_id in set(row["type_id"] for row in rows)}

Upvotes: 0

AKX
AKX

Reputation: 168913

collections.defaultdict is your friend.

collections.defaultdict(list) will automatically create new lists for each key when you index into the defaultdict, so all you need is:

import collections

result = collections.defaultdict(list)
for row in rows:
  result[row['type_id']].append(row)

Upvotes: 5

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