arr = [ { "date": "2022-2-7", "other": [123] },
{ "date": "2022-2-7", "other": [456] },
{ "date": "2022-2-8", "other": [789] } ]
new_dict = {}
for i in arr:
if not i['date'] in new_dict.keys():
new_dict[i['date']] = i['other']
else:
new_dict[i['date']] += i['other']
print(new_dict)>> {'2022-2-7': [123, 456], '2022-2-8': [789]}