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dictionary: sorting the values preserving the order

Hi,
For a particular problem of mine, I want to sort <key, value> pairs
by its value.

Eg:

Input:

A, 4
B, 5
C, 1
D, 2
E, 3

I would like the output to be:

C
D
E
A
B

i.e. I would like to get the keys in the sorted order of values.

I did google around a little bit. One solution to a similar problem
suggested is:

# Courtesy:
http://aspn.activestate.com/ASPN/Pyt...k/Recipe/52306
def sortedDictValues3(adict):
keys = adict.keys()
keys.sort()
return map(adict.get, keys)

This gets a list sorted by the keys. How would I get a revised
dictionary
sorted by its values.

Jul 18 '05 #1
  • viewed: 1826
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5 Replies

hi,

assuming your key-value relationship is one-to-one then as a simple first
pass you can simply initialize d1={} and for i in d.keys(): d1[d[i]] = i
and pass d1 to your sortedDictValue3 function, no?

thanks,
Vikram
On 31 Mar 2005, Rakesh wrote:
Hi,
For a particular problem of mine, I want to sort <key, value> pairs
by its value.

Eg:

Input:

A, 4
B, 5
C, 1
D, 2
E, 3

I would like the output to be:

C
D
E
A
B

i.e. I would like to get the keys in the sorted order of values.

I did google around a little bit. One solution to a similar problem
suggested is:

# Courtesy:
http://aspn.activestate.com/ASPN/Pyt...k/Recipe/52306
def sortedDictValues3(adict):
keys = adict.keys()
keys.sort()
return map(adict.get, keys)

This gets a list sorted by the keys. How would I get a revised
dictionary
sorted by its values.


Jul 18 '05 #2
Rakesh wrote:
Hi,
For a particular problem of mine, I want to sort <key, value> pairs
by its value.

Eg:

Input:

A, 4
B, 5
C, 1
D, 2
E, 3

I would like the output to be:

C
D
E
A
B
the following code does that:
d1 = {'a':4,'b':5,'c':1,'d':2,'e':3}
i1 = [ (d1[i], i) for i in d1.keys() ]
i1.sort()
i1 [(1, 'c'), (2, 'd'), (3, 'e'), (4, 'a'), (5, 'b')] for each in i1:

.... print each[1]
c
d
e
a
b
thanks,
Satchit

i.e. I would like to get the keys in the sorted order of values.

I did google around a little bit. One solution to a similar problem
suggested is:

# Courtesy:
http://aspn.activestate.com/ASPN/Pyt...k/Recipe/52306
def sortedDictValues3(adict):
keys = adict.keys()
keys.sort()
return map(adict.get, keys)

This gets a list sorted by the keys. How would I get a revised
dictionary
sorted by its values.

Jul 18 '05 #3
On 31 Mar 2005 22:40:53 -0800, "Rakesh" <ra***********@yahoo.com>
wrote:
Hi,
For a particular problem of mine, I want to sort <key, value> pairs
by its value.

Eg:

Input:

A, 4
B, 5
C, 1
D, 2
E, 3

I would like the output to be:

C
D
E
A
B

i.e. I would like to get the keys in the sorted order of values.


Generally, dictionaries nearly always have two parts. The dictionary
itself, and a separate list of keys to access it with.

To access the dictionary in a particular order, you just need a sorted
key list.

Since what you want is to access by value, you need to create a second
dictionary with the values as the keys. That will only work if the
values never repeat. If they do, then you need to use a list and not a
dictionary.

This creates a second dictionary with a sorted value key list.

alpha_dict = {'A':4, 'B':5, 'C':1, 'D':2, 'E':3}

# Create a new dictionary with keys and values exchanged.
num_dict = {}
for k in alpha_dict.keys():
num_dict[ alpha_dict[k] ] = k

# Get the num_dict keys and sort them.
num_keys = num_dict.keys()
num_keys.sort()
Ron

Jul 18 '05 #4
Another alternative:

d1 = {'a':4,'b':5,'c':1,'d':2,'e':3*}

il=[(v,k) for k,v in d1.items()]
il.sort()

Jul 18 '05 #5

"Rakesh" <ra***********@yahoo.com> wrote in message
news:11**********************@l41g2000cwc.googlegr oups.com...
This gets a list sorted by the keys.
That is all you *can* get (with the list keys being the dict values).
How would I get a revised dictionary sorted by its values.


You can't. A dictionary is not sorted. The print order is arbitrary and
not controllable.

Terry J. Reedy

Jul 18 '05 #6

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