Path hierarchy tokenizer

The path_hierarchy tokenizer takes a hierarchical value like a filesystem path, splits on the path separator, and emits a term for each component in the tree. The path_hierarcy tokenizer uses Lucene’s PathHierarchyTokenizer underneath.

 POST _analyze {
  "tokenizer": "path_hierarchy",
  "text": "/one/two/three"
}

The above text would produce the following terms:

[ /one, /one/two, /one/two/three ]

The path_hierarchy tokenizer accepts the following parameters:

delimiter

The character to use as the path separator. Defaults to /.

replacement

An optional replacement character to use for the delimiter. Defaults to the delimiter.

buffer_size

The number of characters read into the term buffer in a single pass. Defaults to 1024. The term buffer will grow by this size until all the text has been consumed. It is advisable not to change this setting.

reverse

If true, uses Lucene’s ReversePathHierarchyTokenizer, which is suitable for domain–like hierarchies. Defaults to false.

skip

The number of initial tokens to skip. Defaults to 0.

In this example, we configure the path_hierarchy tokenizer to split on - characters, and to replace them with /. The first two tokens are skipped:

 PUT my-index-000001 {
  "settings": {
    "analysis": {
      "analyzer": {
        "my_analyzer": {
          "tokenizer": "my_tokenizer"
        }
      },
      "tokenizer": {
        "my_tokenizer": {
          "type": "path_hierarchy",
          "delimiter": "-",
          "replacement": "/",
          "skip": 2
        }
      }
    }
  }
}

POST my-index-000001/_analyze
{
  "analyzer": "my_analyzer",
  "text": "one-two-three-four-five"
}

The above example produces the following terms:

[ /three, /three/four, /three/four/five ]

If we were to set reverse to true, it would produce the following:

[ one/two/three/, two/three/, three/ ]

A common use-case for the path_hierarchy tokenizer is filtering results by file paths. If indexing a file path along with the data, the use of the path_hierarchy tokenizer to analyze the path allows filtering the results by different parts of the file path string.

This example configures an index to have two custom analyzers and applies those analyzers to multifields of the file_path text field that will store filenames. One of the two analyzers uses reverse tokenization. Some sample documents are then indexed to represent some file paths for photos inside photo folders of two different users.

 PUT file-path-test {
  "settings": {
    "analysis": {
      "analyzer": {
        "custom_path_tree": {
          "tokenizer": "custom_hierarchy"
        },
        "custom_path_tree_reversed": {
          "tokenizer": "custom_hierarchy_reversed"
        }
      },
      "tokenizer": {
        "custom_hierarchy": {
          "type": "path_hierarchy",
          "delimiter": "/"
        },
        "custom_hierarchy_reversed": {
          "type": "path_hierarchy",
          "delimiter": "/",
          "reverse": "true"
        }
      }
    }
  },
  "mappings": {
    "properties": {
      "file_path": {
        "type": "text",
        "fields": {
          "tree": {
            "type": "text",
            "analyzer": "custom_path_tree"
          },
          "tree_reversed": {
            "type": "text",
            "analyzer": "custom_path_tree_reversed"
          }
        }
      }
    }
  }
}

POST file-path-test/_doc/1
{
  "file_path": "/User/alice/photos/2017/05/16/my_photo1.jpg"
}

POST file-path-test/_doc/2
{
  "file_path": "/User/alice/photos/2017/05/16/my_photo2.jpg"
}

POST file-path-test/_doc/3
{
  "file_path": "/User/alice/photos/2017/05/16/my_photo3.jpg"
}

POST file-path-test/_doc/4
{
  "file_path": "/User/alice/photos/2017/05/15/my_photo1.jpg"
}

POST file-path-test/_doc/5
{
  "file_path": "/User/bob/photos/2017/05/16/my_photo1.jpg"
}

A search for a particular file path string against the text field matches all the example documents, with Bob’s documents ranking highest due to bob also being one of the terms created by the standard analyzer boosting relevance for Bob’s documents.

 GET file-path-test/_search {
  "query": {
    "match": {
      "file_path": "/User/bob/photos/2017/05"
    }
  }
}

It’s simple to match or filter documents with file paths that exist within a particular directory using the file_path.tree field.

 GET file-path-test/_search {
  "query": {
    "term": {
      "file_path.tree": "/User/alice/photos/2017/05/16"
    }
  }
}

With the reverse parameter for this tokenizer, it’s also possible to match from the other end of the file path, such as individual file names or a deep level subdirectory. The following example shows a search for all files named my_photo1.jpg within any directory via the file_path.tree_reversed field configured to use the reverse parameter in the mapping.

 GET file-path-test/_search {
  "query": {
    "term": {
      "file_path.tree_reversed": {
        "value": "my_photo1.jpg"
      }
    }
  }
}

Viewing the tokens generated with both forward and reverse is instructive in showing the tokens created for the same file path value.

 POST file-path-test/_analyze {
  "analyzer": "custom_path_tree",
  "text": "/User/alice/photos/2017/05/16/my_photo1.jpg"
}

POST file-path-test/_analyze
{
  "analyzer": "custom_path_tree_reversed",
  "text": "/User/alice/photos/2017/05/16/my_photo1.jpg"
}

It’s also useful to be able to filter with file paths when combined with other types of searches, such as this example looking for any files paths with 16 that also must be in Alice’s photo directory.

 GET file-path-test/_search {
  "query": {
    "bool" : {
      "must" : {
        "match" : { "file_path" : "16" }
      },
      "filter": {
        "term" : { "file_path.tree" : "/User/alice" }
      }
    }
  }
}