python,list,csv,dictionary , How to find the difference between two lists of dictionaries checking the key-value pair


How to find the difference between two lists of dictionaries checking the key-value pair

Question:

Tag: python,list,csv,dictionary

I've already searched for a solution to my problem but with no success. Part of the solution for my problem is here, but this does not solve it all.

I have two lists of dictionaries like this - each dictionary is written to a csv file but I read the contents to the following variables:

list1 = [{a:1, b:2, c:3}, {a:4, b:5, c:6}, {a:7, b:8, c:9}]
list2 = [{b:2, a:1, c:3}, {c:6, b:5, a:4}, {b:8, a:7, c:9}]

Using the solution of the link above, ie:

>>> import itertools

>>> a = [{'a': '1'}, {'c': '2'}]
>>> b = [{'a': '1'}, {'b': '2'}]
>>> intersec = [item for item in a if item in b]
>>> sym_diff = [item for item in itertools.chain(a,b) if item not in intersec]

I get no matches because the order of the dictionary is different. But in fact, both lists are the same. How can I check this? Do I have to sort the dictionaries before writing them to the csv file? Can this be a solution?

This is my major problem at the moment but I have another issue also. It would be great to be able to make this match check but ignoring one or more keys defined by me. Is this also possible?

EDIT: I have the dicitonaries in a csv file and I'm reading them with the following code:

def read_csv_file(self, filename):
    '''Read CSV file and return its content as a Python list.'''
    f = open(filename, 'r')
    csvfile = csv.reader(f)
    f.close
    return [row for row in csvfile]

This is very important because I think the problem is that after reading the values from the csv it's not dictionaries anymore, so the order has to be the same.

EDIT2: sample of the csv file (3 lines, it's creating an empty line but that's not an issue...)

"{u'Deletion': '0', u'Source': 'Not Applicable', u'Status': ''}"

"{u'Deletion': '0', u'Source': 'Not Applicable', u'Status': ''}"

Answer:

Part of this solution was found by OP as per our last CHAT conversation, it was to convert a string into dictionary using ast module.

Now using this module to convert every row read by the csv.reader() as it returns a list of strings, which would be a list of one string in case of OP's CVS file, then append this dictionary into a list. After that using list comprehension with itertools.chain, we can get the difference between the two lists.

import csv
import ast
import itertools

def csvToList(myCSVFile):

    '''This function is used to convert strings returned by csv.reader() into List of dictionaries'''

        f = open(myCSVFile, 'r')
        l = []
        try:
            reader = csv.reader(f)
            for row in reader:
                if row: #as you mentioned in your 2nd edit that you could have empty rows.
                    l.append(ast.literal_eval(row[0]))
        finally:
            f.close()        
        return l

list1 = csvToList('myCSV1.csv')
list2 = csvToList('myCSV2.csv')

l1_sub_l2  = [d for d in list1 if d not in list2]
l2_sub_l1  = [d for d in list2 if d not in list1]
list_difference = list(itertools.chain(l1_sub_l2, l2_sub_l1))   

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