Cardinality aggregation in Elasticsearch - Mini Project: Build & Apply

Cardinality Aggregation in Elasticsearch

📖 Scenario: You work for an online store that wants to know how many unique customers have placed orders.

🎯 Goal: Build an Elasticsearch query using cardinality aggregation to find the count of unique customer IDs from the orders data.

📋 What You'll Learn

Create an Elasticsearch index named orders with sample order documents

Add a variable for the field name to aggregate on

Write a cardinality aggregation query using the field variable

Print the unique count of customers from the aggregation result

💡 Why This Matters

🌍 Real World

Counting unique customers helps businesses understand how many different people buy their products.

💼 Career

Knowing how to use cardinality aggregation is useful for data analysts and backend developers working with Elasticsearch.

1

Create the orders index with sample data

Create an Elasticsearch index called orders with these exact documents: {"order_id": 1, "customer_id": "C1"}, {"order_id": 2, "customer_id": "C2"}, {"order_id": 3, "customer_id": "C1"}, {"order_id": 4, "customer_id": "C3"}.

Elasticsearch

# Your code here

Need a hint?

Use PUT /orders/_doc/{id} to add each document with the exact fields and values.

2

Set the field name for aggregation

Create a variable called field_name and set it to the string "customer_id".

Elasticsearch

PUT /orders/_doc/1
{
  "order_id": 1,
  "customer_id": "C1"
}

PUT /orders/_doc/2
{
  "order_id": 2,
  "customer_id": "C2"
}

PUT /orders/_doc/3
{
  "order_id": 3,
  "customer_id": "C1"
}

PUT /orders/_doc/4
{
  "order_id": 4,
  "customer_id": "C3"
}

field_name = "customer_id"  # Your code here

Need a hint?

Just assign the string "customer_id" to the variable field_name.

3

Write the cardinality aggregation query

Write an Elasticsearch query using cardinality aggregation on the field stored in field_name. Use the aggregation name unique_customers.

Elasticsearch

PUT /orders/_doc/1
{
  "order_id": 1,
  "customer_id": "C1"
}

PUT /orders/_doc/2
{
  "order_id": 2,
  "customer_id": "C2"
}

PUT /orders/_doc/3
{
  "order_id": 3,
  "customer_id": "C1"
}

PUT /orders/_doc/4
{
  "order_id": 4,
  "customer_id": "C3"
}

field_name = "customer_id"

query = {
    "size": 0,
    "aggs": {
        "unique_customers": {
            "cardinality": {
                "field": field_name
            }
        }
    }
}  # Your code here

Need a hint?

Use "aggs": { "unique_customers": { "cardinality": { "field": field_name }}} inside the query.

4

Print the unique customer count from the aggregation result

Print the unique customer count from the aggregation result using print(result['aggregations']['unique_customers']['value']).

Elasticsearch

PUT /orders/_doc/1
{
  "order_id": 1,
  "customer_id": "C1"
}

PUT /orders/_doc/2
{
  "order_id": 2,
  "customer_id": "C2"
}

PUT /orders/_doc/3
{
  "order_id": 3,
  "customer_id": "C1"
}

PUT /orders/_doc/4
{
  "order_id": 4,
  "customer_id": "C3"
}

field_name = "customer_id"

query = {
    "size": 0,
    "aggs": {
        "unique_customers": {
            "cardinality": {
                "field": field_name
            }
        }
    }
}

result = {
    "aggregations": {
        "unique_customers": {
            "value": 3
        }
    }
}

print(result['aggregations']['unique_customers']['value'])  # Your code here

Need a hint?

Use the print statement to show the value inside result['aggregations']['unique_customers']['value'].