Expression Columns

Expression columns compute values using Jinja2 expressions that can reference other columns. This powerful feature allows you to create derived columns, combine data from multiple sources, and implement complex business logic.

Before You Start

Before getting started, ensure you have the Data Designer client and configuration builder set up:

import os
from nemo_microservices import NeMoMicroservices
from nemo_microservices.beta.data_designer import DataDesignerClient, DataDesignerConfigBuilder
from nemo_microservices.beta.data_designer.config import columns as C
from nemo_microservices.beta.data_designer.config import params as P

data_designer_client = DataDesignerClient(
    client=NeMoMicroservices(base_url=os.environ["NEMO_MICROSERVICES_BASE_URL"])
)

config_builder = DataDesignerConfigBuilder(model_configs="path/to/your/model_configs.yaml")

---

String Concatenation

Combine text from multiple columns:

Simplified API

config_builder.add_column(
    name="full_address",
    type="expression",
    expr="{{ street_address }}, {{ city }}, {{ state }} {{ zip_code }}"
)

Typed API

config_builder.add_column(
    C.ExpressionColumn(
        name="full_address",
        expr="{{ street_address }}, {{ city }}, {{ state }} {{ zip_code }}"
    )
)

Mathematical Operations

Perform calculations with numeric columns:

Simplified API

# Calculate area from length and width
config_builder.add_column(
    name="area",
    type="expression",
    expr="{{ length * width }}"
)

# Calculate percentage
config_builder.add_column(
    name="discount_percentage",
    type="expression",
    expr="{{ (original_price - sale_price) / original_price * 100 }}"
)

Typed API

# Calculate area from length and width
config_builder.add_column(
    C.ExpressionColumn(
        name="area",
        expr="{{ length * width }}"
    )
)

# Calculate percentage
config_builder.add_column(
    C.ExpressionColumn(
        name="discount_percentage",
        expr="{{ (original_price - sale_price) / original_price * 100 }}"
    )
)

Conditional Logic

Use Jinja2 conditional statements:

Simplified API

config_builder.add_column(
    name="shipping_cost",
    type="expression",
    expr="{% if order_total > 50 %}0{% else %}5.99{% endif %}"
)

# More complex conditional
config_builder.add_column(
    name="customer_tier",
    type="expression",
    expr="""
    {%- if total_purchases > 1000 -%}
    Premium
    {%- elif total_purchases > 500 -%}
    Gold
    {%- elif total_purchases > 100 -%}
    Silver
    {%- else -%}
    Bronze
    {%- endif -%}
    """
)

Typed API

config_builder.add_column(
    C.ExpressionColumn(
        name="shipping_cost",
        expr="{% if order_total > 50 %}0{% else %}5.99{% endif %}"
    )
)

# More complex conditional
config_builder.add_column(
    C.ExpressionColumn(
        name="customer_tier",
        expr="""
        {%- if total_purchases > 1000 -%}
        Premium
        {%- elif total_purchases > 500 -%}
        Gold
        {%- elif total_purchases > 100 -%}
        Silver
        {%- else -%}
        Bronze
        {%- endif -%}
        """
    )
)

Person Attribute Expressions

When using person samplers, you can reference person attributes in expressions:

Setup person sampler:

config_builder.with_person_samplers({"customer": {"locale": "en_US"}})

Reference person attributes:

Simplified API

config_builder.add_column(
    name="customer_full_name",
    type="expression",
    expr="{{ customer.first_name }} {{ customer.last_name }}"
)

config_builder.add_column(
    name="welcome_message",
    type="expression",
    expr="Welcome {{ customer.first_name }}! You're from {{ customer.city }}, {{ customer.state }}."
)

Typed API

config_builder.add_column(
    C.ExpressionColumn(
        name="customer_full_name",
        expr="{{ customer.first_name }} {{ customer.last_name }}"
    )
)

config_builder.add_column(
    C.ExpressionColumn(
        name="welcome_message",
        expr="Welcome {{ customer.first_name }}! You're from {{ customer.city }}, {{ customer.state }}."
    )
)

Data Type Conversion

Expression columns can specify output data types:

Simplified API

config_builder.add_column(
    name="total_items",
    type="expression",
    expr="{{ quantity_a + quantity_b }}",
    convert_to="int"  # Convert result to integer
)

config_builder.add_column(
    name="is_eligible",
    type="expression",
    expr="{{ age >= 18 }}",
    convert_to="bool"  # Convert result to boolean
)

Typed API

config_builder.add_column(
    C.ExpressionColumn(
        name="total_items",
        expr="{{ quantity_a + quantity_b }}",
        convert_to="int"
    )
)

config_builder.add_column(
    C.ExpressionColumn(
        name="is_eligible",
        expr="{{ age >= 18 }}",
        convert_to="bool"
    )
)

For more detailed information about Jinja2 templating, see the Using Jinja Templates guide.