Character filters in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this character filter configuration?

Given the following Elasticsearch analyzer configuration using a mapping character filter, what will be the output tokens for the input text "foo-bar baz"?

Elasticsearch

{
  "analysis": {
    "char_filter": {
      "my_mapping": {
        "type": "mapping",
        "mappings": ["- => ""]"]
      }
    },
    "analyzer": {
      "my_analyzer": {
        "type": "custom",
        "char_filter": ["my_mapping"],
        "tokenizer": "whitespace"
      }
    }
  }
}

A ["foobar", "baz"]

B ["foo-bar", "baz"]

C ["foo", "bar", "baz"]

D ["foo", "-bar", "baz"]

💡 Hint

Think about what the mapping character filter does to the dash (-) character before tokenization.

The mapping character filter replaces the dash (-) with an empty string, so "foo-bar" becomes "foobar" before the whitespace tokenizer splits the text. Thus, the tokens are ["foobar", "baz"].

🧠 Conceptual

intermediate

Which character filter type removes HTML tags from input text?

In Elasticsearch, which character filter type is designed to remove HTML tags from the input text before tokenization?

A mapping

B keyword_marker

C html_strip

D pattern_replace

💡 Hint

Think about the filter that cleans HTML content.

The html_strip character filter removes HTML tags from the input text, cleaning it before tokenization.

❓ Predict Output

advanced

What error does this character filter configuration cause?

Consider this Elasticsearch character filter configuration snippet. What error will Elasticsearch raise when trying to create this analyzer?

Elasticsearch

{
  "analysis": {
    "char_filter": {
      "bad_filter": {
        "type": "mapping",
        "mappings": "- >"
      }
    },
    "analyzer": {
      "test_analyzer": {
        "type": "custom",
        "char_filter": ["bad_filter"],
        "tokenizer": "standard"
      }
    }
  }
}

A IllegalArgumentException because 'mappings' must be an array

B ElasticsearchParseException due to invalid mapping syntax

C No error, analyzer created successfully

D NullPointerException during analysis

💡 Hint

Check the syntax of the mapping string.

The mapping string "- >" is invalid because the mapping syntax requires '=>' to separate the source and target characters. This causes an ElasticsearchParseException.

🚀 Application

advanced

How many tokens are produced by this analyzer?

Given this analyzer configuration with a pattern_replace character filter that removes digits, how many tokens will be produced from the input "abc123 def456 ghi789"?

Elasticsearch

{
  "analysis": {
    "char_filter": {
      "remove_digits": {
        "type": "pattern_replace",
        "pattern": "\\d",
        "replacement": ""
      }
    },
    "analyzer": {
      "digit_remover": {
        "type": "custom",
        "char_filter": ["remove_digits"],
        "tokenizer": "whitespace"
      }
    }
  }
}

A 6

B 0

C 1

D 3

💡 Hint

Digits are removed before tokenization, but spaces remain.

The pattern_replace filter removes all digits, so the input becomes "abc def ghi". The whitespace tokenizer splits on spaces, producing 3 tokens.

🔧 Debug

expert

Why does this analyzer produce unexpected tokens?

An Elasticsearch analyzer uses this character filter configuration but produces tokens with underscores instead of spaces. What is the cause?

Elasticsearch

{
  "analysis": {
    "char_filter": {
      "underscore_to_space": {
        "type": "mapping",
        "mappings": ["_ => \\u0020"]
      }
    },
    "analyzer": {
      "custom_analyzer": {
        "type": "custom",
        "char_filter": ["underscore_to_space"],
        "tokenizer": "whitespace"
      }
    }
  }
}

A The mapping syntax requires double backslashes for unicode escapes

B The mapping character filter does not support unicode escapes

C The mapping uses an incorrect unicode escape sequence for space

D The tokenizer is ignoring the character filter

💡 Hint

Check how JSON strings handle backslashes.

In JSON, backslashes must be escaped. The mapping string "_ => \u0020" is interpreted literally, not as a space. It should be "_ => \\u0020" to represent the unicode space character correctly.