Python dictionary values merging based on specific key

Question

I want to merge two CSV files that I have read into python using the following code,

a = csv.DictReader(csv1)
b = csv.DictReader(csv2)

aMap = {}
bMap = {}

for row in a:
    aMap[row['id']] = row

for row in b:
    bMap[row['id']] = row

Now I should have two dictionaries whose keys are the 'id' field from the two CSVs. What I want to do is take everything from the aMap and add the values to the corresponding key values to bMap. For example in aMap, a key in the dictionary looks like this,

'123456' : {'name': 'SomeName', 'type': 'someType'}

And what I have in bMap is

'123456' : {'location' : 'someLocation'}

And what I want is,

'123456' : {'location' : 'someLocation', 'name' : 'SomeName', 'type' : 'someType'}

Is there a specific function for this or do I have to create a new dictionary? Something similar to update() but just appending values instead of updating.

unutbu · Accepted Answer · 2011-10-24 18:37:44Z

1

You could use one collections.defaultdict, and use update to merge rows from csv2.

import collections

aMap = collections.defaultdict(dict)

for row in csv.DictReader(csv1):
    aMap[row['id']] = row

for row in csv.DictReader(csv2):
    aMap[row['id']].update(row)

answered Oct 24, 2011 at 18:37

unutbu

886k197 gold badges1.9k silver badges1.7k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Evgeny · Accepted Answer · 2011-10-24 18:21:14Z

0

I don't think there is a builtin function for that. So you'll have to do something like

def AppendToValues(from_map, to_map):
  for key in from_map:
    to_map[key] = to_map.get(key, {})
    to_map.update(from_map.get(key, {}))

To delete key, value from map:

del my_map[key]

answered Oct 24, 2011 at 18:21

Evgeny

3,2942 gold badges21 silver badges21 bronze badges

1 Comment

user611105 Over a year ago

Ah balls, I figured as much. =/ I'll give your function a go and see how it goes :)

Bryce · Accepted Answer · 2011-10-24 18:31:22Z

0

I believe you can use the defaultdict in the collections module for this. http://docs.python.org/library/collections.html#collections.defaultdict

I think the examples are pretty close to being exactly what you want.

answered Oct 24, 2011 at 18:31

Bryce

3202 silver badges9 bronze badges

Collectives™ on Stack Overflow

Python dictionary values merging based on specific key

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related