# DTC Snippets

## Splits

### One block per day

```yaml
Split: datetime.strptime('source.start_time', "%d %m %Y") != datetime.strptime('start_time', "%d %m %Y")
```

### One block per session\_id

```yaml
Split: source.session_id != BlockAggregateName.session_id
```

### Inactivity based split

```yaml
Split: (time - end_time).minutes > 30
# Calculates the distance in minutes between event time and the end time (time last event was received) of the current block.  Split happens when the difference is greater than 30 minutes.
```

## Advanced DTC functions

### Create a map

```yaml
  - Name: id_to_value
    Type: map
    Value: BlockAggregateName.id_to_value.set(source.id, source.value)
```

### Merge 2 strings with comma separated values in source data to create a list of tuples

```yaml
Fields:
  - Name: products_bought
    Type: list
    Value: item_stats.products_bought.extend(list(zip([val.strip() for val in source.item_id.split(',')], [float(val.strip()) for val in source.value.split(',')])))
    # This creates a list of tuples [(item_id1, value1), (item_id2, value2)...]
    When: source.event_name = 'ecommerce_purchase' and source.currency = 'usd'
```

## Data cleansing

### Create a boolean value from a condition on a text field in raw data

```yaml
- Name: fb_connected
  Type: boolean
  Value: True if source.signin_method == 'fb' else False
```

### Convert strings in raw data to a float

If the raw data has a field `"txn_amount": "9.99"`, which is a float but formatted as a string, it can be converted to a float to perform operations in a field value

```yaml
- Name: purchase_amount
  Type: float
  Value: float(source.txn_amount) + game_stats.purchase_amount
  When: source.event_id == 'purchase' and source.purchase_source == 'offer'
```

### Flatten a list of list of tuples

```yaml
Fields:
  - Name: products_bought
    Type: list
    Value: [item for sublist in source.products_bought for item in sublist]
    # Flattens the list of list of tuples of products_bought
```

## Data validation

## Determine correctness of a BlockAggregate

One possible way of determining the correctness of a BlockAggregate (like a user session, for example), without relying on the order of events could be done with:

```yaml
- Name: game_start_and_end
  Type: list
  Value: session_stats.game_start_and_end.add((time, source.event_id))
  When: source.event_id == 'game_start' or source.event_id == 'game_end'
```

Then another field can be defined to determine the correctness:

```yaml
-  Name: valid_session
  Type: boolean
  Value: valid_start_and_end(session_stats.game_start_and_end)
  When: source.event_id == 'game_start' or source.event_id == 'game_end'
```

`valid_start_and_end` is defined as a custom function.

```yaml
def valid_start_and_end(games_list):
  # Determine that each game_start has a corresponding game_end.
  # and return True / False accordingly.
```

As more events are processed the value of session\_stats.valid\_session will maintain whether this session is valid or not. The fields are evaluated in the order they are defined so the valid\_session field should be defined after game\_start\_and\_end field.

## Per event validation

Some ways to validate individual events for things like missing field values, reuse fields etc are:

* Create a variable (`VariableAggregate`) with the required clean up on the event field
* Use `When` in `Field` for validation conditions
* Define a `valid_event` field and use that in When. This can be go in `VariableAggregate` if we don't want to save it
* If it is ok to ignore fields that have errors (e.g. missing), Blurr does not process the event and drops it as default behavior. If the source is missing event fields, the `Field evaluation` is skipped and an error is logged in debug logs.
