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Python Discussion Thread
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Sep 15th, 2009

Combining Multiple Element Dictionaries

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I am trying to combine two multi-element dictionaries but am running into a problem.

From the example below, what I expected was the dictionary x to contain all three unique combinations.

What seems to have happened is that the y dictionary overwrote the x dictionary.

Am I just using this wrong? Is there a elegant way to add two multi element dictionaies?
thanks!

Python Syntax (Toggle Plain Text)
>>> x=nested_dict()
>>> y=nested_dict()
>>> 
>>> x[1][1]=1
>>> x[1][2]=2
>>> y[1][3]=3
>>> x.update(y)
>>> print x
defaultdict(<class 'nested_dict.nested_dict'>, {1: defaultdict(<class 'nested_dict.nested_dict'>, {3: 3})})
>>> x=nested_dict()
>>> y=nested_dict()
>>> 
>>> x[1][1]=1
>>> x[1][2]=2
>>> y[1][3]=3
>>> x.update(y)
>>> print x
defaultdict(<class 'nested_dict.nested_dict'>, {1: defaultdict(<class 'nested_dict.nested_dict'>, {3: 3})})

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chase32

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Sep 15th, 2009

Re: Combining Multiple Element Dictionaries

This is correct, as you are updating x[1], that is y's key is also 1 and so overwrite's whatever is in x for that key. Change to
y[2][3]=3
or use
x[1].update(y[1])
and you should get what you expect.. If that's not satisfactory then you will have to write your own routine to update however you want.

woooee

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Sep 16th, 2009

Re: Combining Multiple Element Dictionaries

Thanks!

the

Python Syntax (Toggle Plain Text)
x[1].update(y[1])
x[1].update(y[1])

format should work.

If I walk through the keys of Y and use the same value for the key of X, that should let me merge two arbitrary two element dictionaries

chase32

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Sep 16th, 2009

Re: Combining Multiple Element Dictionaries

Indeed it should, but test for "key in x" as well, or use a try/except, as you can never tell. Please mark this "solved" so no wastes their time on a solved thread.

Edit: I just did the following and it worked fine so you don't have to test for "key in x" as update takes care of that for you.

Python Syntax (Toggle Plain Text)
x = {}
x[1] = {}
x[1][1]=1
x[1][2]=2
 
y = {}
y[2] = {}
y[2][3]=3
x.update(y)
print x
#
# prints
{1: {1: 1, 2: 2}, 2: {3: 3}}
x = {}
x[1] = {}
x[1][1]=1
x[1][2]=2

y = {}
y[2] = {}
y[2][3]=3
x.update(y)
print x
#
# prints
{1: {1: 1, 2: 2}, 2: {3: 3}}

Last edited by woooee; Sep 16th, 2009 at 1:13 am.

woooee

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Sep 16th, 2009

Re: Combining Multiple Element Dictionaries

Marked as solved. Thanks for the help!

chase32

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Sep 16th, 2009

Re: Combining Multiple Element Dictionaries

This is what I ended up with, works great

Python Syntax (Toggle Plain Text)
def merge(lib1,lib2):
    for item in lib2.keys():
        lib1[item].update(lib2[item])
    return lib1
def merge(lib1,lib2):
    for item in lib2.keys():
        lib1[item].update(lib2[item])
    return lib1

Last edited by chase32; Sep 16th, 2009 at 1:22 pm.

chase32

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Sep 16th, 2009

Re: Combining Multiple Element Dictionaries

Click to Expand / Collapse Quote originally posted by chase32 ...

This is what I ended up with, works great
Python Syntax (Toggle Plain Text)
def merge(lib1,lib2):
    for item in lib2.keys():
        lib1[item].update(lib2[item])
    return lib1
def merge(lib1,lib2): for item in lib2.keys(): lib1[item].update(lib2[item]) return lib1

Mild caveat, for this to work lib1 and lib2 have to be of type collections.defaultdict(dict) , and each value has to be a dictionary too.

Here is a typical eaxmple ...

python Syntax (Toggle Plain Text)
# merge two dictionaries and handle key collisions with 
# collections.defaultdict(dict)
 
import collections
 
def merge(lib1, lib2):
    for item in lib2.keys():
        lib1[item].update(lib2[item])
    return lib1
 
d1 = {'a':{1:11}, 'b':{2:22}, 'c':{3:33}}
d2 = {'d':{4:44}, 'c':{5:55}, 'e':{6:66}}
 
# mutliple values go into a dictionary
lib1 = collections.defaultdict(dict)
lib2 = collections.defaultdict(dict)
 
# convert each dict to a defaultdict
lib1.update(d1)
lib2.update(d2)
 
print(lib1)
print(lib2)
print('-'*60)
print( merge(lib1, lib2) )
 
"""my result (notice key 'c')-->
defaultdict(<type 'dict'>, {'a': {1: 11}, 'c': {3: 33}, 'b': {2: 22}})
defaultdict(<type 'dict'>, {'c': {5: 55}, 'e': {6: 66}, 'd': {4: 44}})
------------------------------------------------------------
defaultdict(<type 'dict'>, {'a': {1: 11}, 'c': {3: 33, 5: 55}, 
'b': {2: 22}, 'e': {6: 66}, 'd': {4: 44}})
"""
# merge two dictionaries and handle key collisions with 
# collections.defaultdict(dict)

import collections

def merge(lib1, lib2):
    for item in lib2.keys():
        lib1[item].update(lib2[item])
    return lib1

d1 = {'a':{1:11}, 'b':{2:22}, 'c':{3:33}}
d2 = {'d':{4:44}, 'c':{5:55}, 'e':{6:66}}

# mutliple values go into a dictionary
lib1 = collections.defaultdict(dict)
lib2 = collections.defaultdict(dict)

# convert each dict to a defaultdict
lib1.update(d1)
lib2.update(d2)

print(lib1)
print(lib2)
print('-'*60)
print( merge(lib1, lib2) )

"""my result (notice key 'c')-->
defaultdict(<type 'dict'>, {'a': {1: 11}, 'c': {3: 33}, 'b': {2: 22}})
defaultdict(<type 'dict'>, {'c': {5: 55}, 'e': {6: 66}, 'd': {4: 44}})
------------------------------------------------------------
defaultdict(<type 'dict'>, {'a': {1: 11}, 'c': {3: 33, 5: 55}, 
'b': {2: 22}, 'e': {6: 66}, 'd': {4: 44}})
"""

Last edited by vegaseat; Sep 16th, 2009 at 2:25 pm.

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