Getting values from keys and Viceversa

[psbasha]

Hi,

Dictionary works in getting values from the key values.But I would like to get keys from values.

For example :

d = {100: [1,0,0],102: [0,1,0],202: [0,1,1]}

d.get(102)

o/p: [0,1,0]

I need

i/p

[0,1,0]

o/p : 102

Thanks

PSB

[bartonc]

Hi,

Dictionary works in getting values from the key values.But I would like to get keys from values.

For example :

d = {100: [1,0,0],102: [0,1,0],202: [0,1,1]}

d.get(102)

o/p: [0,1,0]

I need

i/p

[0,1,0]

o/p : 102

Thanks

PSB

Keeping an inverse dictionary is not uncommon:

>>> d = {'a':1, 'b':2, 'c':3}
>>> di = dict((v, k) for k, v in d.items())
>>> di
{1: 'a', 2: 'b', 3: 'c'}
>>>

[psbasha]

Thanks for the reply.

How to handle the dictionary when we have a Key as a number and Values are list?

As I mentioned in my example

-PSB

[psbasha]

Sample>>> d = {100: [1,0,0],102: [0,1,0],202: [0,1,1]}
>>> di = dict((v, k) for k, v in d.items())

Traceback (most recent call last):
  File "<pyshell#9>", line 1, in -toplevel-
    di = dict((v, k) for k, v in d.items())
TypeError: list objects are unhashable
>>>

I am getting the above error when I applied for the example I mentioned

-PSB

[bvdet]

Sample>>> d = {100: [1,0,0],102: [0,1,0],202: [0,1,1]}
>>> di = dict((v, k) for k, v in d.items())

Traceback (most recent call last):
  File "<pyshell#9>", line 1, in -toplevel-
    di = dict((v, k) for k, v in d.items())
TypeError: list objects are unhashable
>>>

I am getting the above error when I applied for the example I mentioned

-PSB

Try this:

>>> dict(zip([str(x) for x in d.values()], d.keys()))
{'[0, 1, 1]': 202, '[1, 0, 0]': 100, '[0, 1, 0]': 102}
>>>

Lists are not hashable but strings are.

[ghostdog74]

Hi,

Dictionary works in getting values from the key values.But I would like to get keys from values.

For example :

d = {100: [1,0,0],102: [0,1,0],202: [0,1,1]}

d.get(102)

o/p: [0,1,0]

I need

i/p

[0,1,0]

o/p : 102

Thanks

PSB

usually, the way to get values is through the values() method.
for this case, you can use the dictionary values() method.
eg

if  [0,1,0] in d.values():
    print "found "

[psbasha]

Try this:

>>> dict(zip([str(x) for x in d.values()], d.keys()))
{'[0, 1, 1]': 202, '[1, 0, 0]': 100, '[0, 1, 0]': 102}
>>>

Lists are not hashable but strings are.

So we have to create the list as string and use it for inversing and use it.

Thanks in advance
PSB

[bartonc]

So we have to create the list as string and use it for inversing and use it.

Thanks in advance
PSB

Not if you use tuples instead of lists.
Lists let you assign into them (they are mutable) as in

aList[index] = valuse

Tuples do not all item assignment. As long as you assign x, y, z all at the same time, as in

pt = x, y, z

you can use tuples.

>>> d = {'a':(1,2,3),'b':(4,5,6),'c':(7,8,9)}
>>> di = dict((v, k) for k, v in d.items())
>>> di
{(4, 5, 6): 'b', (7, 8, 9): 'c', (1, 2, 3): 'a'}
>>>

[bvdet]

Not if you use tuples instead of lists.
Lists let you assign into them (they are mutable) as in

aList[index] = valuse

Tuples do not all item assignment. As long as you assign x, y, z all at the same time, as in

pt = x, y, z

you can use tuples.

>>> d = {'a':(1,2,3),'b':(4,5,6),'c':(7,8,9)}
>>> di = dict((v, k) for k, v in d.items())
>>> di
{(4, 5, 6): 'b', (7, 8, 9): 'c', (1, 2, 3): 'a'}
>>>

Good work Barton. I didn't think of tuples.

>>> d = {100: [1,0,0],102: [0,1,0],202: [0,1,1]}
>>> dict(zip([tuple(x) for x in d.values()], d.keys()))
{(0, 1, 0): 102, (0, 1, 1): 202, (1, 0, 0): 100}
>>>

[bartonc]

Good work Barton. I didn't think of tuples.

>>> d = {100: [1,0,0],102: [0,1,0],202: [0,1,1]}
>>> dict(zip([tuple(x) for x in d.values()], d.keys()))
{(0, 1, 0): 102, (0, 1, 1): 202, (1, 0, 0): 100}
>>>

Take values() and keys() from a dictionary separately scares me a little. But I suppose that there's no reason for the dict to be re-orderd until a new item is add or an old one removed...

[bvdet]

Take values() and keys() from a dictionary separately scares me a little. But I suppose that there's no reason for the dict to be re-orderd until a new item is add or an old one removed...

That never bothered me until you mentioned it. Thinking about it - both d.keys() and d.values() are lists (ordered) so there should be no reason for the 'items' to misalign.