delete dict in list from dict in list

Question

I have two lists (with dicts in it):

old_device_data_list = [{'_id': ObjectId('5f48c8e34545fac49fbff5'), 'device_id': 5, 'time': datetime.datetime(2020, 8, 26, 9, 5, 39, 827000), 'values': {'count': 100, 'late': 0, 'max': 0, 'min': 0, 'on_time': 100, 'sum': 100}}]

result = [{'_id': ObjectId('5f48c8e3997640fac49fbff5'), 'device_id': 5, 'time': datetime.datetime(2020, 8, 26, 9, 5, 39, 827000), 'values': {'count': 100, 'late': 0, 'max': 0, 'min': 0, 'on_time': 100, 'sum': 100}}, {'_id': ObjectId('5f48c8e3997640fac49fbff6'), 'device_id': 4, 'time': datetime.datetime(2020, 8, 26, 9, 5, 39, 827000), 'values': {'count': 180, 'late': 0, 'max': 0, 'min': 0, 'on_time': 180, 'sum': 180}}, {'_id': ObjectId('5f48c8e3997640fac49fbff8'), 'device_id': 3, 'time': datetime.datetime(2020, 8, 27, 9, 5, 39, 827000), 'values': {'count': 50, 'late': 0, 'max': 0, 'min': 0, 'on_time': 50, 'sum': 50}}, {'_id': ObjectId('5f48c8e3997640fac49fbff7'), 'device_id': 4, 'time': datetime.datetime(2020, 8, 27, 9, 5, 39, 827000), 'values': {'count': 120, 'late': 0, 'max': 0, 'min': 0, 'on_time': 120, 'sum': 120}}, {'_id': ObjectId('5f48c8e3997640fac49fbff9'), 'device_id': 3, 'time': datetime.datetime(2020, 8, 28, 9, 5, 39, 827000), 'values': {'count': 210, 'late': 0, 'max': 0, 'min': 0, 'on_time': 210, 'sum': 210}}]

I want to delete the dicts from the old_device_data_list out of the result list. I tried it with numpy with:

numpy.setdiff1d(result, old_device_data_list)

Then I got error:

TypeError: '<' not supported between instances of 'dict' and 'dict'

Answer 1

The description of numpy.setdiff1d says:

Return the sorted, unique values in ar1 that are not in ar2 .

In order to sort the values, it needs to compare them using the < operator. But dictionaries cannot be compared like this. The relation "smaller than" is not defined for dictionaries.

NumPy is designed for working with numeric values, not for arbitrary Python data structures.

You could use a simple list comprehension to create a list of those dictionaries that are in result but not in old_device_data_list :

result = [d for d in result if d not in old_device_data_list]