How to properly group data by time boundaries?

Question

PostgreSQL

Good afternoon.
We have a model with sample data

id  DateTime                  Value
133 "2015-04-17 12:12:54 +04" 23
134 "2015-04-17 12:13:54 +04" 23
135 "2015-04-17 12:23:54 +04" 23
136 "2015-04-17 12:44:54 +04" 25
137 "2015-04-17 14:52:54 +04" 42
138 "2015-04-17 15:45:54 +04" 42

We need to query all records whose DateTime does not overlap with the nearest records within 15 minutes.
Ie 133 is suitable
136 is suitable because 44 - 23 > 15 minutes
137 and 138 yes the rest are not.
This is probably a clustering task, that is, you need to form groups of records with boundaries of 15 minutes. If more than 15 minutes, then this is a new cluster. The problem is that I don't know how to implement it in the form of a correct algorithm :/.
You probably need something like this.
Pseudo python code

last_row_date_time = datetime.datetime()
groups = [] #Distinct groups
for row in Data.objects.all().order_by('datetime')
     if (row.datetime - last_row_date_time) > datetime.timedelta(minutes=15)
         groups.append(row)
         print "New group"
     else:
         print "Old group"

But I don't understand how correct this is. Perhaps there are some better ways to solve the problem?

Answer 1

To begin with, I will start from the fact that you have some kind of journal and all entries are in ascending time. For simplicity, I assume that you have these records in an array.
The decision in a forehead - to organize search. Step by step:

1. We take element N
   You will separately need to think about what to do if you work with the first and last element, because in this case, one of your semi_ variables will definitely be false.

Answer 2

If the variable -+15 minutes does not change and you don’t have a huge amount of data in the database now and you can rewrite adding them, then:
The current data in the database can be clustered stupidly by running it through python, I think any algorithm can be, not the point.
And cluster new records when adding:
before adding a new record, make a selection of records that are "+ -15 minutes from now".
Check the found records for the presence of groups:
If there are groups, then look for those in which all records are "+ -15 minutes from now", if not found, then create a new one and bind the record.
A group is an M2M connection.
You may need some locks at the time of adding and searching for groups.
The solution that immediately came to mind may have missed something.