Filter aggregation in Elasticsearch - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a filter aggregation in Elasticsearch?

A filter aggregation lets you count or analyze documents that match a specific filter condition, like counting only documents with a certain field value.

beginner

How do you define a filter aggregation in an Elasticsearch query?

You define it by specifying a filter with a query inside the aggregation, like "filter": { "term": { "status": "active" } }.

intermediate

Can filter aggregation be combined with other aggregations?

Yes! You can nest other aggregations inside a filter aggregation to analyze only the filtered documents further.

intermediate

What is the difference between filter aggregation and filters aggregation?

Filter aggregation uses one filter to select documents. Filters aggregation lets you define multiple filters and get results for each filter separately.

beginner

Example: What does this filter aggregation do?

{
  "aggs": {
    "active_users": {
      "filter": { "term": { "status": "active" } }
    }
  }
}

It counts how many documents have the field status set to active. The result is the number of active users.

What does a filter aggregation do in Elasticsearch?

A Deletes documents matching a filter

B Counts documents matching a filter

C Updates documents matching a filter

D Sorts documents by a field

Filter aggregation counts or analyzes documents that match a specific filter condition.

Which key is used to specify the filter in a filter aggregation?

A "filter"

B "query"

C "match"

D "term"

The "filter" key defines the filter condition inside a filter aggregation.

Can you nest other aggregations inside a filter aggregation?

A Yes

B No

C Only in filters aggregation

D Only with terms aggregation

You can nest other aggregations inside a filter aggregation to analyze filtered documents further.

What is the main difference between filter and filters aggregations?

A Filter is faster than filters

B Filter sorts documents; filters counts documents

C Filter updates documents; filters deletes documents

D Filter uses one filter; filters uses multiple filters

Filter aggregation applies one filter; filters aggregation applies multiple filters separately.

In this filter aggregation, what does it count?

{
  "filter": { "term": { "status": "active" } }
}

A All documents

B Documents with status inactive

C Documents with status active

D Documents without status field

It counts documents where the field "status" equals "active".

Explain how filter aggregation works in Elasticsearch and give a simple example.

Think about how you count only certain documents using a filter.

Describe the difference between filter aggregation and filters aggregation.

One uses one filter, the other uses many filters at once.

Practice

1. What is the main purpose of a filter aggregation in Elasticsearch?

easy

A. To delete documents matching a query

B. To sort documents by a field value

C. To update documents in the index

D. To select documents that match a specific condition

Solution

1. Step 1: Understand filter aggregation role

   A filter aggregation is used to select documents that meet a certain condition or criteria.

2. Step 2: Compare with other options

   Sorting, updating, or deleting documents are not functions of filter aggregation.

3. Final Answer:

   To select documents that match a specific condition -> Option D

4. Quick Check:

   Filter aggregation = select matching documents [OK]

Hint: Filter aggregation selects matching documents only [OK]

Common Mistakes:

• Confusing filter aggregation with sorting
• Thinking filter aggregation modifies documents
• Mixing filter aggregation with delete operations

2. Which of the following is the correct syntax to define a filter aggregation in an Elasticsearch query?

easy

A. "aggs": { "my_filter": { "filter": { "term": { "status": "active" } } } }

B. "aggs": { "my_filter": { "terms": { "field": "status" } } }

C. "aggs": { "my_filter": { "range": { "field": "age", "gte": 30 } } }

D. "aggs": { "my_filter": { "match": { "status": "active" } } }

Solution

1. Step 1: Identify filter aggregation syntax

   The filter aggregation uses the key "filter" with a query inside, like "term" for exact match.

2. Step 2: Check each option

   "aggs": { "my_filter": { "filter": { "term": { "status": "active" } } } } correctly uses "filter" with a "term" query. Options A, C, and D use other aggregation types or query types incorrectly.

3. Final Answer:

   "aggs": { "my_filter": { "filter": { "term": { "status": "active" } } } } -> Option A

4. Quick Check:

   Filter aggregation syntax = option with "filter" key [OK]

Hint: Filter aggregation always uses "filter" key inside aggs [OK]

Common Mistakes:

• Using "terms" instead of "filter" for filter aggregation
• Confusing query types inside aggregation
• Missing the "filter" key in aggregation

3. Given this Elasticsearch aggregation query snippet, what will be the count of documents in the filter aggregation named active_users?

{
  "aggs": {
    "active_users": {
      "filter": { "term": { "status": "active" } }
    }
  }
}

Assuming the index has 1000 documents, 300 of which have status set to active.

medium

A. 300

B. 1000

C. 700

D. 0

Solution

1. Step 1: Understand filter aggregation result

   The filter aggregation counts documents matching the filter condition, here "status" = "active".

2. Step 2: Apply given data

   Out of 1000 documents, 300 have status "active", so the aggregation count is 300.

3. Final Answer:

   300 -> Option A

4. Quick Check:

   Filter count = matching docs = 300 [OK]

Hint: Filter aggregation count = number of matching documents [OK]

Common Mistakes:

• Choosing total documents instead of filtered count
• Confusing filter aggregation with terms aggregation count
• Assuming zero if filter is not exact

4. Identify the error in this filter aggregation query:

{
  "aggs": {
    "filtered_data": {
      "filter": {
        "terms": {
          "status": "active"
        }
      }
    }
  }
}

medium

A. The filter aggregation must use "term" not "terms" for single value

B. The "terms" query requires an array of values, not a single string

C. The aggregation name "filtered_data" is invalid

D. The filter aggregation cannot be nested inside "aggs"

Solution

1. Step 1: Check the "terms" query usage

   The "terms" query expects an array of values, e.g., ["active"], not a single string.

2. Step 2: Validate other parts

   The aggregation name is valid, and filter aggregation can be inside "aggs". Using "term" is an alternative but not an error here.

3. Final Answer:

   The "terms" query requires an array of values, not a single string -> Option B

4. Quick Check:

   "terms" query needs array, not string [OK]

Hint: "terms" query needs array of values, not single string [OK]

Common Mistakes:

• Using string instead of array for "terms" query
• Thinking aggregation names have restrictions
• Believing filter aggregation can't be nested

5. You want to find the average price of products only in the category "electronics" using filter aggregation. Which of the following query snippets correctly combines filter aggregation with an average sub-aggregation?

hard

A. {
"query": { "term": { "category": "electronics" } },
"aggs": { "avg_price": { "avg": { "field": "price" } } }
}

B. {
"aggs": {
"avg_price": { "avg": { "field": "price" } },
"filter": { "term": { "category": "electronics" } }
}
}

C. {
"aggs": {
"electronics_filter": {
"filter": { "term": { "category": "electronics" } },
"aggs": { "avg_price": { "avg": { "field": "price" } } }
}
}
}

D. {
"aggs": {
"electronics_filter": {
"terms": { "field": "category" },
"aggs": { "avg_price": { "avg": { "field": "price" } } }
}
}
}

Solution

1. Step 1: Understand filter aggregation with sub-aggregation

   Filter aggregation uses "filter" key and can contain sub-aggregations inside "aggs".

2. Step 2: Check each option

   { "aggs": { "electronics_filter": { "filter": { "term": { "category": "electronics" } }, "aggs": { "avg_price": { "avg": { "field": "price" } } } } } } correctly nests an average aggregation inside a filter aggregation for category "electronics". { "aggs": { "avg_price": { "avg": { "field": "price" } }, "filter": { "term": { "category": "electronics" } } } } misplaces filter outside aggregation. { "query": { "term": { "category": "electronics" } }, "aggs": { "avg_price": { "avg": { "field": "price" } } } } uses query filtering, not aggregation filtering. { "aggs": { "electronics_filter": { "terms": { "field": "category" }, "aggs": { "avg_price": { "avg": { "field": "price" } } } } } } uses "terms" aggregation, not filter.

3. Final Answer:

   { "aggs": { "electronics_filter": { "filter": { "term": { "category": "electronics" } }, "aggs": { "avg_price": { "avg": { "field": "price" } } } } } } -> Option C

4. Quick Check:

   Filter aggregation with sub-aggregation = { "aggs": { "electronics_filter": { "filter": { "term": { "category": "electronics" } }, "aggs": { "avg_price": { "avg": { "field": "price" } } } } } } [OK]

Hint: Nest avg aggregation inside filter aggregation's "aggs" [OK]

Common Mistakes:

• Placing filter outside aggregation block
• Using query filter instead of filter aggregation
• Confusing terms aggregation with filter aggregation