Pattern tokenizer

Pattern tokenizer

The pattern tokenizer uses a regular expression to either split text into terms whenever it matches a word separator, or to capture matching text as terms.

The default pattern is \W+, which splits text whenever it encounters non-word characters.

Beware of Pathological Regular Expressions

The pattern tokenizer uses Java Regular Expressions.

A badly written regular expression could run very slowly or even throw a StackOverflowError and cause the node it is running on to exit suddenly.

Read more about pathological regular expressions and how to avoid them.

Example output

resp = client.indices.analyze(
    tokenizer="pattern",
    text="The foo_bar_size's default is 5.",
)
print(resp)

response = client.indices.analyze(
  body: {
    tokenizer: 'pattern',
    text: "The foo_bar_size's default is 5."
  }
)
puts response

const response = await client.indices.analyze({
  tokenizer: "pattern",
  text: "The foo_bar_size's default is 5.",
});
console.log(response);

POST _analyze
{
  "tokenizer": "pattern",
  "text": "The foo_bar_size's default is 5."
}

The above sentence would produce the following terms:

[ The, foo_bar_size, s, default, is, 5 ]

Configuration

The pattern tokenizer accepts the following parameters:

Example configuration

In this example, we configure the pattern tokenizer to break text into tokens when it encounters commas:

resp = client.indices.create(
    index="my-index-000001",
    settings={
        "analysis": {
            "analyzer": {
                "my_analyzer": {
                    "tokenizer": "my_tokenizer"
                }
            },
            "tokenizer": {
                "my_tokenizer": {
                    "type": "pattern",
                    "pattern": ","
                }
            }
        }
    },
)
print(resp)
resp1 = client.indices.analyze(
    index="my-index-000001",
    analyzer="my_analyzer",
    text="comma,separated,values",
)
print(resp1)

response = client.indices.create(
  index: 'my-index-000001',
  body: {
    settings: {
      analysis: {
        analyzer: {
          my_analyzer: {
            tokenizer: 'my_tokenizer'
          }
        },
        tokenizer: {
          my_tokenizer: {
            type: 'pattern',
            pattern: ','
          }
        }
      }
    }
  }
)
puts response
response = client.indices.analyze(
  index: 'my-index-000001',
  body: {
    analyzer: 'my_analyzer',
    text: 'comma,separated,values'
  }
)
puts response

const response = await client.indices.create({
  index: "my-index-000001",
  settings: {
    analysis: {
      analyzer: {
        my_analyzer: {
          tokenizer: "my_tokenizer",
        },
      },
      tokenizer: {
        my_tokenizer: {
          type: "pattern",
          pattern: ",",
        },
      },
    },
  },
});
console.log(response);
const response1 = await client.indices.analyze({
  index: "my-index-000001",
  analyzer: "my_analyzer",
  text: "comma,separated,values",
});
console.log(response1);

PUT my-index-000001
{
  "settings": {
    "analysis": {
      "analyzer": {
        "my_analyzer": {
          "tokenizer": "my_tokenizer"
        }
      },
      "tokenizer": {
        "my_tokenizer": {
          "type": "pattern",
          "pattern": ","
        }
      }
    }
  }
}
POST my-index-000001/_analyze
{
  "analyzer": "my_analyzer",
  "text": "comma,separated,values"
}

The above example produces the following terms:

[ comma, separated, values ]

In the next example, we configure the pattern tokenizer to capture values enclosed in double quotes (ignoring embedded escaped quotes \"). The regex itself looks like this:

"((?:\\"|[^"]|\\")*)"

And reads as follows:

• A literal "

• Start capturing:

  • A literal \" OR any character except "
  • Repeat until no more characters match

• A literal closing "

When the pattern is specified in JSON, the " and \ characters need to be escaped, so the pattern ends up looking like:

\"((?:\\\\\"|[^\"]|\\\\\")+)\"

resp = client.indices.create(
    index="my-index-000001",
    settings={
        "analysis": {
            "analyzer": {
                "my_analyzer": {
                    "tokenizer": "my_tokenizer"
                }
            },
            "tokenizer": {
                "my_tokenizer": {
                    "type": "pattern",
                    "pattern": "\"((?:\\\\\"|[^\"]|\\\\\")+)\"",
                    "group": 1
                }
            }
        }
    },
)
print(resp)
resp1 = client.indices.analyze(
    index="my-index-000001",
    analyzer="my_analyzer",
    text="\"value\", \"value with embedded \\\" quote\"",
)
print(resp1)

response = client.indices.create(
  index: 'my-index-000001',
  body: {
    settings: {
      analysis: {
        analyzer: {
          my_analyzer: {
            tokenizer: 'my_tokenizer'
          }
        },
        tokenizer: {
          my_tokenizer: {
            type: 'pattern',
            pattern: '"((?:\\\"|[^"]|\\\")+)"',
            group: 1
          }
        }
      }
    }
  }
)
puts response
response = client.indices.analyze(
  index: 'my-index-000001',
  body: {
    analyzer: 'my_analyzer',
    text: '"value", "value with embedded \" quote"'
  }
)
puts response

const response = await client.indices.create({
  index: "my-index-000001",
  settings: {
    analysis: {
      analyzer: {
        my_analyzer: {
          tokenizer: "my_tokenizer",
        },
      },
      tokenizer: {
        my_tokenizer: {
          type: "pattern",
          pattern: '"((?:\\\\"|[^"]|\\\\")+)"',
          group: 1,
        },
      },
    },
  },
});
console.log(response);
const response1 = await client.indices.analyze({
  index: "my-index-000001",
  analyzer: "my_analyzer",
  text: '"value", "value with embedded \\" quote"',
});
console.log(response1);

PUT my-index-000001
{
  "settings": {
    "analysis": {
      "analyzer": {
        "my_analyzer": {
          "tokenizer": "my_tokenizer"
        }
      },
      "tokenizer": {
        "my_tokenizer": {
          "type": "pattern",
          "pattern": "\"((?:\\\\\"|[^\"]|\\\\\")+)\"",
          "group": 1
        }
      }
    }
  }
}
POST my-index-000001/_analyze
{
  "analyzer": "my_analyzer",
  "text": "\"value\", \"value with embedded \\\" quote\""
}

The above example produces the following two terms:

[ value, value with embedded \" quote ]