Combine list of dictionaries based on particular key value

Question

I am newbie with Python and I am trying to solve this problem in a script.

I have 2 lists of dictionaries as follows:

en_list = [{'time': 840, 'text': "I want to introduce you to some\nvery wise kids that I've known,"}, 
           {'time': 5480, 'text': 'but first I want\nto introduce you to a camel.'}, 
           {'time': 8720, 'text': 'This is Cassie, a therapy camel\nvisiting one of our young patients'}, 
           {'time': 13000, 'text': 'in her room,'},
           {'time': 14920, 'text': 'which is pretty magical.'}]

fr_list = [{'time': 840, 'text': "Je veux vous présenter certains enfants\ntrès sages que j'ai rencontrés,"},
           {'time': 5480, 'text': 'mais je veux commencer\npar vous présenter un chameau.'},
           {'time': 8720, 'text': 'Voici Cassie, un chameau thérapeutique qui\nrend visite à une de nos jeunes patients'},
           {'time': 14920, 'text': 'ce qui est plutôt magique.'}]

I want to create a new list with only matching values of the 'time' key.

I came up with this, but apparently it doesn't take the time key into consideration although it works just fine if both lists are having the same number of dictionaries.

for i, m in enumerate(zip(en_list, fr_list), start=1):
    print(i, m[0], "=", m[1])

This prints out the following:

1 {'time': 840, 'text': "I want to introduce you to some\nvery wise kids that I've known,"} = {'time': 840, 'text': "Je veux vous présenter certains enfants\ntrès sages que j'ai rencontrés,"}
2 {'time': 5480, 'text': 'but first I want\nto introduce you to a camel.'} = {'time': 5480, 'text': 'mais je veux commencer\npar vous présenter un chameau.'}
3 {'time': 8720, 'text': 'This is Cassie, a therapy camel\nvisiting one of our young patients'} = {'time': 8720, 'text': 'Voici Cassie, un chameau thérapeutique qui\nrend visite à une de nos jeunes patients'}
4 {'time': 13000, 'text': 'in her room,'} = {'time': 14920, 'text': 'ce qui est plutôt magique.'}

As you can see, it wrongly mapped the English with 'time': 13000 to the French with 'time': 14920 although the English list has the correct text with the same time, but the code above ignored it.

The desired output should include all items with the matching value of 'time' key and ignore the non-matching items. How can I achieve this?

Thanks in advance for your support!

Answer 1

Your solution, as you said, doesn't take the time values into consideration. To craft a working solution for this, we need to get the time values for each list, find out which ones they have in common, then filter the original lists based on common time values.

# Make set of time values for given list.
get_times = lambda l: {d['time'] for d in l}
# Intersection of sets
times_shared = get_times(en_list) & get_times(fr_list)

# Get dicts whose time value is shared.
get_shared = lambda l: [d for d in l if d['time'] in times_shared]

for i, m in enumerate(zip(get_shared(en_list), get_shared(fr_list)), start=1):
    print(i, m[0], '=', m[1])

---

Or you could convert the lists to dicts first (pairs of time: text), which makes it much more straightforward:

makedict = lambda l: {d['time']: d['text'] for d in l}
en_dict = makedict(en_list)
fr_dict = makedict(fr_list)

# Intersection
times_shared = set(en_dict) & set(fr_dict)

for i, time in enumerate(times_shared, start=1):
    print('%d %d %r = %r' % (i, time, en_dict[time], fr_dict[time]))

---

Update Jun 1 2020: My code above has some bad practice, like named lambdas and l as a variable name. Also I forgot to sort times_shared. I might rewrite the second solution like this:

en, fr = ({d['time']: d['text'] for d in lst} for lst in [en_list, fr_list])

# Intersection
times_shared = sorted(set(en) & set(fr))

for i, time in enumerate(times_shared, start=1):
    print('%d %d %r = %r' % (i, time, en[time], fr[time]))

Answer 2

Make a list from each dict, including all of the time values. Find the times common to both lists (making another list). Iterate through this list of common times, printing the corresponding dict from each of your two lists.

Each of these steps is a common programming technique covered in tutorials and other Stack Overflow questions. Coding is left as an exercise for the student.

Answer 3

list(filter(lambda item: item[0].get('time') == item[1].get('time'), zip(en_list, fr_list)))

(EDITED): Maybe this will work

result = []
for k, en in enumerate(en_list):
    for fr in fr_list:
        if en.get('time') == fr.get('time'):
            result.append({k: '{} = {}'.format(en, fr)})