How to split array into another based on attribute value?

Question

I have an array that contains several type of dict, as example:

arr = [
    {'type': 'employee.update', ...}, 
    {'type': 'job.started', ...}, 
    {'type': 'meeting.xpto', ...}
    ...
]

How can I split the "main" array by prefix of type? Is necessary to iterate over entire array for every prefix?

employess_actions = list(filter(lambda x: x['type'].startswith('employee.'), arr))
job_actions = list(filter(lambda x: x['type'].startswith('job.'), arr))
meeting_actions = list(filter(lambda x: x['type'].startswith('meeting.'), arr))

Is there any performatic way of achieve it? Or a pythonic way.

Wouldn't it simpler to just loop over arr ?

Paolo
– Paolo

2020-07-05 14:39:34 +00:00
Commented Jul 5, 2020 at 14:39 — Paolo
– Paolo, Commented Jul 5, 2020 at 14:39

trincot · Accepted Answer · 2020-07-05 14:44:34Z

2

You could use a (default)dict for collecting the elements by prefix:

from collections import defaultdict
result = defaultdict(list)
for o in arr:
    result[o["type"][:o["type"].index(".")]].append(o)

This assumes of course that all those types have a "." in them.

For example, if:

arr = [
    {"type": "employee.update"}, 
    {"type": "job.started"}, 
    {"type": "meeting.xpto"},
    {"type": "job.ended"}
]

then the resulting result is

{
  "employee": [{"type": "employee.update"}],
  "job":      [{"type": "job.started"}, {"type": "job.ended"}],
  "meeting":  [{"type": "meeting.xpto"}]
}

answered Jul 5, 2020 at 14:44

trincot

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Comments

RoadRunner · Accepted Answer · 2020-07-05 14:58:06Z

You could iterate over arr, group each type with a collections.defaultdict using the the prefix as the key. We can use str.split() to split the type on ., then unpack the prefix using tuple unpacking.

from collections import defaultdict

arr = [
    {'type': 'employee.update'}, 
    {'type': 'job.started'}, 
    {'type': 'meeting.xpto'}
]

types = defaultdict(list)
for dic in arr:
    prefix, _ = dic["type"].split(".")
    types[prefix].append(dic)

print(types)

Output:

defaultdict(<class 'list'>, {'employee': [{'type': 'employee.update'}], 'job': [{'type': 'job.started'}], 'meeting': [{'type': 'meeting.xpto'}]})

If we want to only append the type and not the full dictionary:

types[prefix].append(dic["type"])

Which will give instead:

defaultdict(<class 'list'>, {'employee': ['employee.update'], 'job': ['job.started'], 'meeting': ['meeting.xpto']})

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