Dictionaries

[Lad]

How can I add two dictionaries into one?
E.g.
a={'a:1}
b={'b':2}

I need

the result {'a':1,'b':2}.

Is it possible?

Thank you
L.

[Simon Brunning]

Re: Dictionaries

On 18 Oct 2006 08:24:27 -0700, Lad <python@hope.cz wrote:

How can I add two dictionaries into one?
E.g.
a={'a:1}
b={'b':2}
>
I need
>
the result {'a':1,'b':2}.

>>a={'a':1}
>>b={'b':2}
>>a.update(b)
>>a

{'a': 1, 'b': 2}

--
Cheers,
Simon B
simon@brunningo nline.net

http://www.brunningonline.net/simon/blog/

[Gary Herron]

Re: Dictionaries

Lad wrote:

How can I add two dictionaries into one?
E.g.
a={'a:1}
b={'b':2}
>
I need
>
the result {'a':1,'b':2}.
>
Is it possible?
>
Thank you
L.
>
>

Yes, use update. Beware that this modifies a dictionary in place rather
than returning a new dictionary.

>>a={'a':1}
>>b={'b':2}
>>a.update(b)
>>a

{'a': 1, 'b': 2}

Gary Herron

[Tim Chase]

Re: Dictionaries

How can I add two dictionaries into one?

E.g.
a={'a:1}
b={'b':2}
>
I need
>
the result {'a':1,'b':2}.

>>a.update(b)
>>a

{'a':1,'b':2}

-tkc

[Boris Borcic]

Re: Dictionaries


dict(a.items() + b.items())

Lad wrote:

How can I add two dictionaries into one?
E.g.
a={'a:1}
b={'b':2}
>
I need
>
the result {'a':1,'b':2}.
>
Is it possible?

[Steven D'Aprano]

Re: Dictionaries

On Wed, 18 Oct 2006 08:24:27 -0700, Lad wrote:

How can I add two dictionaries into one?
E.g.
a={'a:1}
b={'b':2}
>
I need
>
the result {'a':1,'b':2}.
>
Is it possible?

What should the result be if both dictionaries have the same key?

a={'a':1, 'b'=2}
b={'b':3}

should the result be:
{'a':1, 'b'=2} # keep the existing value
{'a':1, 'b'=3} # replace the existing value
{'a':1, 'b'=[2, 3]} # keep both values
or something else?

Other people have already suggested using the update() method. If you want
more control, you can do something like this:

def add_dict(A, B):
"""Add dictionaries A and B and return a new dictionary."""
C = A.copy() # start with a copy of A
for key, value in B.items():
if C.has_key(key):
raise ValueError("dup licate key '%s' detected!" % key)
C[key] = value
return C


--
Steven.

[Lad]

Re: Dictionaries


Tim Chase wrote:

How can I add two dictionaries into one?
E.g.
a={'a:1}
b={'b':2}

I need

the result {'a':1,'b':2}.

>

>>a.update(b)
>>a

{'a':1,'b':2}
>
-tkc

Thank you ALL for help.
However It does not work as I would need.
Let's suppose I have

a={'c':1,'d':2}
b={'c':2}
but
a.update(b)
will make
{'c': 2, 'd': 2}

and I would need
{'c': 3, 'd': 2}

(because `c` is 1 in `a` dictionary and `c` is 2 in `b` dictionary, so
1+2=3)

How can be done that?
Thank you for the reply
L

[Tim Chase]

Re: Dictionaries

However It does not work as I would need.

Let's suppose I have
>
a={'c':1,'d':2}
b={'c':2}
but
a.update(b)
will make
{'c': 2, 'd': 2}
>
and I would need
{'c': 3, 'd': 2}

Ah...a previously omitted detail.

There are likely a multitude of ways to do it. However, the one
that occurs to me off the top of my head would be something like

dict((k, a.get(k, 0) + b.get(k, 0)) for k in a.keys()+b.keys ())


If the sets are huge, you can use itertools

>>from itertools import chain
>>dict((k, a.get(k, 0) + b.get(k, 0)) for k in

chain(a.keys(), b.keys()))
{'c': 3, 'd': 2}

which would reduce the need for creating the combined dictionary,
only to throw it away.

-tkc

[Lad]

Re: Dictionaries


Steven,
Thank you for your reply and question.

>
What should the result be if both dictionaries have the same key?

The answer: the values should be added together and assigned to the key
That is
{'a':1, 'b':5}
( from your example below)

Is there a solution?
Thanks for the reply
L.

>
a={'a':1, 'b'=2}
b={'b':3}
>
should the result be:
{'a':1, 'b'=2} # keep the existing value
{'a':1, 'b'=3} # replace the existing value
{'a':1, 'b'=[2, 3]} # keep both values
or something else?
>
Other people have already suggested using the update() method. If you want
more control, you can do something like this:
>
def add_dict(A, B):
"""Add dictionaries A and B and return a new dictionary."""
C = A.copy() # start with a copy of A
for key, value in B.items():
if C.has_key(key):
raise ValueError("dup licate key '%s' detected!" % key)
C[key] = value
return C
>
>
--
Steven.

[Rob De Almeida]

Re: Dictionaries

Lad wrote:

Let's suppose I have
>
a={'c':1,'d':2}
b={'c':2}
but
a.update(b)
will make
{'c': 2, 'd': 2}
>
and I would need
{'c': 3, 'd': 2}
>
(because `c` is 1 in `a` dictionary and `c` is 2 in `b` dictionary, so
1+2=3)
>
How can be done that?

dict([(k, a.get(k, 0) + b.get(k,0)) for k in set(a.keys() + b.keys())])

[Fredrik Lundh]

Re: Dictionaries

Lad wrote:

The answer: the values should be added together and assigned to the key
That is
{'a':1, 'b':5}
( from your example below)
>
Is there a solution?

have you tried coding a solution and failed, or are you just expecting
people to code for free?

</F>

[Steven D'Aprano]

Re: Dictionaries

On Wed, 18 Oct 2006 09:31:50 -0700, Lad wrote:

>
Steven,
Thank you for your reply and question.
>

>>
>What should the result be if both dictionaries have the same key?

The answer: the values should be added together and assigned to the key
That is
{'a':1, 'b':5}
( from your example below)
>
Is there a solution?

Of course there is a solution. You just have to program it.

Look again at my example code before:

def add_dict(A, B):
"""Add dictionaries A and B and return a new dictionary."""
C = A.copy() # start with a copy of A
for key, value in B.items():
if C.has_key(key):
raise ValueError("dup licate key '%s' detected!" % key)
C[key] = value
return C


Can you see how to modify this function to do what you want?

(Hint: instead of raising a ValueError exception, you want to do something
else.)


--
Steven.

[Gary Herron]

Re: Dictionaries

Fredrik Lundh wrote:

Lad wrote:
>
>

>The answer: the values should be added together and assigned to the key
>That is
>{'a':1, 'b':5}
>( from your example below)
>>
>Is there a solution?
>>

>
have you tried coding a solution and failed, or are you just expecting
people to code for free?
>
</F>
>
>

Right. This thread begins to look like someone with a homework
assignment asking for code rather than attempting to try programming it
up himself. I was happy to answer the first plea for help, but I'd be
leery of providing any actual code.

Gary Herron

[Lad]

Re: Dictionaries

Steven,
Thank you for help;
Here is a code that works in a way I need


A={'c':1,'d':2, 'e':3,'f':2}
B={'c':2,'e':1}
if len(A)>=len(B):
Delsi=B
C = A.copy()
else:
Delsi=A
C = B.copy()

for key, value in Delsi.items():
if C.has_key(key):
C[key]=C[key]+value
else:
C[key]=value



How easy :-)
Regards,
L.

Steven D'Aprano wrote:

On Wed, 18 Oct 2006 09:31:50 -0700, Lad wrote:
>

Steven,
Thank you for your reply and question.

>
What should the result be if both dictionaries have the same key?

The answer: the values should be added together and assigned to the key
That is
{'a':1, 'b':5}
( from your example below)

Is there a solution?

>
Of course there is a solution. You just have to program it.
>
Look again at my example code before:
>
def add_dict(A, B):
"""Add dictionaries A and B and return a new dictionary."""
C = A.copy() # start with a copy of A
for key, value in B.items():
if C.has_key(key):
raise ValueError("dup licate key '%s' detected!" % key)
C[key] = value
return C
>
>
Can you see how to modify this function to do what you want?
>
(Hint: instead of raising a ValueError exception, you want to do something
else.)
>
>
--
Steven.