First-Last

First-Last features are great for enrichments of fields from one-to-many relations. It is commonly used to enrich an entity with fields of the first or last appearance of a one-to-many related assets or entities.

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Simple first-last feature

In this example, we define simple first-last features for the entity customer:

# customer.yml

features:
- type: first_last
  name: last_call_agent_id
  data_type: string
  asset: db_prod.core.phone_call_dim
  options:
    method: last
    sort_by: created_at
    field: agent_id
  filters: null

type

The feature type. In case of first-last features, it should be set to first_last.

name

Give the feature a name.

asset

The data asset with the field to be added as feature to our entity. asset should be the full path: "db.schema.name".

asset has to be related to our entity (see related data asset).

join_name [optional]

In case multiple join patterns are defined between an entity and a data asset, join_name is used to determine which join path to use for a specific feature.

For more information about using multiple join paths between an entity and a data asset, visit the related data assets page.

data_type [optional]

Specify the feature data type. If no data_type specified, Lynk will assume the data type is string.

The options for data types are:

string

For any type of string data type

number

For any type of number data type. For example: integer, float, decimal etc..

datetime

For any type of time-based data type. For example: date, timestamp, datetime etc..

bool

For boolean data type.

time_field [optional]

Specifies which asset time field to use in case of time-based aggregation is applied to the first-last feature. If not specified, Lynk will use the asset's default time_field.

See time aggregation for more information on how time fields are being used for time-based feature aggregations.

options

The options for the first-last definitions on which field we would like to get and how to sort the related data asset

method

Determines which instance of the data asset to retrieve - the first or the last, based on the sort_by option.

sort_by

The data asset field to sort by.

field

The name of the data asset field to retrieve as the entity feature.

offset

Use offset to choose the second, third or other field values with an offset from the start or from the end of the sorted list

Offset - Example 1

Enriching the customer entity with the order_status of the third order, ordered by created_at:

# customer.yml

features:
- type: first_last
  name: second_order_status
  data_type: string
  asset: db_prod.core.orders
  options:
    method: first
    sort_by: created_at
    field: order_status
    offset: 3
  filters: null

Offset - Example 2

Enriching the customer entity with the order status of the second order from the last (one before the last order), ordered by created_at:

# customer.yml

features:
- type: first_last
  name: second_order_status
  data_type: string
  asset: db_prod.core.orders
  options:
    method: last
    sort_by: created_at
    field: order_status
    offset: 2
  filters: null

filters

Custom filters to be applied on the data asset. See filters page for in depth information on how to apply filters.

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Understanding First-Last Features

In case we have a many-to-one relationship between a Data Asset and an Entity, and we need to enrich the entity with a field from the Data Asset without aggregating it - we can't just take the field - we need to define which occurrence to take. This is when we should use first-last features.

To better understand how First-Last features work, look the following diagram;

First Last Feature Diagram

The above diagram shows an example when a customer (entity) has many orders (data asset). That means, each customer may be associated with more than one row in db.schema.orders.

In this case, we took the field total_price of the last order, sorted by order_date, and added it to the customer entity as a feature.