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Preserve Dictionary Order

 

Preserve Dictionary Order, How do I keep the order of my dictionary
reyno2ac

4 Oct, 2009 - 07:41 PM
Post #1

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Joined: 10 Sep, 2009
Posts: 4


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I'm extremely new to python, so please go easy on me.

I'm trying to take the values from two dictionaries and compute their sums. For example:
A = {1:4, 5:2, 6:3, 8:7}
B = {2:1, 4:4, 7:5, 9:2}
The result should be [5, 9, 6, 8].

For some reason the program is outputting [9, 5, 6, 8].

CODE

def sparse_add():
    A = {1:4, 5:2, 6:3, 8:7}
    B = {2:1, 4:4, 7:5, 9:2}
    i = 0
    ab_total = {}
    a_list = []
    b_list = []
    
    #converts A and B to lists
    a_list = A.values()
    b_list = B.values()
    
    #adds A and B to ab_total
    if len(a_list) == len(b_list):
        while i < len(a_list):
            ab_total[i] = a_list[i] + b_list[i]
            i = i+1
    else:
        print "Your vectors do not contain an even amount of elements"

    print "The new dictionary is:", ab_total
    print "The sum of the dictionaries is:", ab_total.values()
    #should print 5, 6, 8, 9

if __name__ == '__main__':
    sparse_add()
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Nallo

RE: Preserve Dictionary Order

5 Oct, 2009 - 03:21 AM
Post #2

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Joined: 19 Jul, 2009
Posts: 24



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The order of the items (key, value pairs) in dictionaries is not preserved.

So if you need the values in a certain order there are serveral ways:

1. Dont put them in a dictionary in the first place, use a list or a tuple
2. If your keys are ordered you can iterate over the keys (after you sorted them) insted of values:
CODE
def add(dic1, dic2):
    key1, key2 = dic1.keys(), dic2.keys()

    #now lets get back the order
    key1.sort()
    key2.sort()
    

    total = []
    for i, j in zip(key1, key2):
        #total is a list here, I dont see reason to make it a dict
        total.append(dic1[key1] + dic2[key2])

    return total
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