CODEWITHSUNDEEP
python
MaxB
MaxB

Reputation: 458

Comparing two un-ordered lists for differences in individual elements

Given two lists:

listA = ['A' , 'B' , 'C, D' , 'E, F, G', 'H' , 'I']

listB = ['C' , 'E, G' , 'A' , 'B' , 'I']

I want to compare each element and highlight the differences where it is applicable.

listA['E,F,G'] and listB['E,G'].

The difference would be ['F']

There are several differences between the individual list elements and ideally would like to flag them all. Is this possible with python? Is the below thinking correct? 

set(listA).intersection(listB)

Upvotes: 2

Views: 95

Answers (4)

Slayer
Slayer

Reputation: 882

What you are looking for is symmetric difference. In python you can achieve it by using symmetric_difference function or using short hand s ^ t.

s.symmetric_difference(t)

This will give you the difference elements. Now, what you can do is 

def split_words(element):
   if len(element) > 1:
      element = element.split(',')
   return element

result = []
for e1, e2 in zip(sorted(list_a), sorted(list_b)):
    if e1 not in list_b:
       e1 = split_words(e1)
       e2 = split_words(e2)

       diff = set(e1) ^ set(e2)
       result.append(diff)

Upvotes: 4

ncica
ncica

Reputation: 7206

listA = ['E','F','G']
listB = ['E','G']

use list comprehension

diff2 = [y for y in listA if y not in listB]
print (diff2)

output: ['F']

or

diff1=[]
for item in listA:
    if item not in listB:
        diff1.append(item)
print (diff1)

output: ['F']

Upvotes: 1

tobias_k
tobias_k

Reputation: 82929

From comments, it seems like you want to "unpack" the nested pseudo-string-lists before calculating the difference. You could define a simple helper function for that.

>>> listA = ['A' , 'B' , 'C, D' , 'E, F, G', 'H' , 'I']
>>> listB = ['C' , 'E, G' , 'A' , 'B' , 'I']
>>> elements = lambda s: set(x for y in s for x in y.split(", "))
>>> elements(listA)
{'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I'}

Then, you can use set operations like -, ^, &, or | to get what you want.

>>> elements(listA) - elements(listB) # difference
{'D', 'F', 'H'}
>>> elements(listA) ^ elements(listB) # sym. diff.
{'D', 'F', 'H'}
>>> elements(listA) & elements(listB) # intersection
{'A', 'B', 'C', 'E', 'G', 'I'}
>>> elements(listA) | elements(listB) # union
{'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I'}

Upvotes: 3

paragnomen
paragnomen

Reputation: 31

Intersection is a common part of sets. If you want a difference of sets just use... a difference method. E.g.:

list(set(listA) - set(listB))

or:

list(set(listA).difference(set(listB)))

Upvotes: 1

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