find difference of values between 2 array of objects in python

Question

I have 2 array of objects:

a = [{'a': 1, 'b': 2}, {'c': 3, 'd': 4}, {'e': 5, 'f': 6}]
b = [{'a': 1, 'b': 2}, {'g': 3, 'h': 4}, {'f': 6, 'e': 5}]

Output:
a - b = [{'c': 3, 'd': 4}] ("-" symbol is only for representation, showing difference. Not mathematical minus.)
b - a = [{'g': 3, 'h': 4}]

In every array, the order of key may be different. I can try following and check for that:

for i in range(len(a)):
   current_val = a[i]
   for x, y in current_val.items:
      //search x keyword in array b and compare it with b

but this approach doesn't feel right. Is there simpler way to do this or any utility library which can do this similar to fnc or pydash?

there is no 'a-b' for lists. but output of `a-b` is not what you wrote. it should contain `{'e':5,'f':6}` — Shoaib Mirzaei, Feb 03 '21 at 07:51
why dont you try to transfer a,b like ```a ={"a-3,b-2","c-3,d-4"...}``` use set to subtraction them — pepper, Feb 03 '21 at 07:53

score 1 · Accepted Answer · answered Feb 03 '21 at 07:54

1

You can use lambda:

g = lambda a,b : [x for x in a if x not in b]

g(a,b) # a-b

[{'c': 3, 'd': 4}]

g(b,a) # b-a

[{'g': 3, 'h': 4}]

answered Feb 03 '21 at 07:54

Pygirl

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1

Hi @Pygirl... your soultion looks more pythonic. Thanks – undefined Feb 03 '21 at 08:00

score 1 · Answer 2 · answered Feb 03 '21 at 07:54

Just test if all elements are in the other array

a = [{'a': 1, 'b': 2}, {'c': 3, 'd': 4}, {'e': 5, 'f': 6}]
b = [{'a': 1, 'b': 2}, {'g': 3, 'h': 4}, {'f': 6, 'e': 5}]


def find_diff(array_a, array_b):
    diff = []
    for e in array_a:
        if e not in array_b:
            diff.append(e)
    return diff

print(find_diff(a, b))
print(find_diff(b, a))

the same with list comprehension

def find_diff(array_a, array_b):
    return [e for e in array_a if e not in array_b]

score 1 · Answer 3 · answered Feb 03 '21 at 07:54

here is the code for subtracting list of dictionaries

a = [{'a': 1, 'b': 2}, {'c': 3, 'd': 4}, {'e': 6, 'f': 6}]
b = [{'a': 1, 'b': 2}, {'g': 3, 'h': 4}, {'f': 6, 'e': 6}]
a_b = []
b_a = []
for element in a:
    if element not in b:
        a_b.append( element )
for element in b:
    if element not in a:
        b_a.append( element )
print("a-b =",a_b)
print("b-a =",b_a)

find difference of values between 2 array of objects in python

3 Answers3