# R Help - Search

The R help integration in StatET includes an advanced, fast search engine for the help pages of the R packages installed in an R environment.

The handling of the R help search is similar to the workflow of most other searches in Eclipse. A search is entered in the 'R Help' tab in the Search dialog, which is accessible for example via the button in the R help view or, in most perspectives, the 'Search' dropdown button in the toolbar. The search results are shown structured and sortable in a new page of the Search view. Then one can open selected pages in the R Help view.

To enable the search functionality, the R environment must be indexed.

## Standard Search

The R help search page provides three standard modes to search for help pages:

- Topics/Alias (strict): The text must match exactly a topic of the page. This is comparable to a simple call of `help("searchtopic")` in R.
- Selected Fields: The text is searched with tolerance in the selected page field(s).
- Complete Document: This is a classic full text search, the text is searched with tolerance in the complete text of the help page.

The matching with tolerance is comparable with the known internet search engines. That means most flections of words and punctuation mark are ignored.

Additionally, the search can be filtered by selected packages or an R help keyword. If the search text is empty, this options allow to show all help pages of the selected packages or tagged with the specified keyword.

## Advanced Query Syntax

The R help search is powered by the Apache Lucene library, which also allows several options to perform advanced customized searches. This section describes the syntax for queries typed in the search text field.

### Terms

A query is broken up into terms and operators. There are two types of terms: Single Terms and Phrases.

A Single Term is a single word such as "test" or "hello".

A Phrase is a group of words surrounded by double quotes such as "hello dolly".

Multiple terms can be combined together with Boolean operators to form a more complex query. The AND operator is the default conjunction operator. This means that if there is no Boolean operator between two terms, a help document have to match both terms.

### Fields

Lucene supports fielded data. When performing a search you can either specify a field, or use the default field(s). For field names and the default field(s) for R help search see table below.

You can search any field by typing the field name followed by a colon ":" and then the term you are looking for.

As an example, let's assume a Lucene index contains two fields, title and text and text is the default field. If you want to find the document entitled "The Right Way" which contains the text "don't go this way", you can enter:

    title:"The Right Way" AND text:go

or

    title:"The Right Way" AND go

Since text is the default field, the field indicator is not required.

#### Fields for R Help Pages

`pkg` | the exact name of the package
`page` | the exact name of the page
`alias` | an exact alias/topic of the page (1)
`alias.txt` | an alias/topic of the page (2)
`title.txt` | the title of the page (2, 3)
`concept.txt` | a concept of the page (2)
`keyword` | a keyword of the page
`descr.txt` | the description section of the page (3)
`doc.txt` | the main content of the page except the title, description and examples section (3)
`examples.txt` | the examples section of the page (3)

Default field(s) depends on the selected R help search mode: (1) = "Topics/Alias (strict)", (2) = "Selected Field" (only the selected fields) and (3) = "Complete Document".

### Term Modifiers

Lucene supports modifying query terms to provide a wide range of searching options.

#### Wildcard Searches

Lucene supports single and multiple character wildcard searches within single terms (not within phrase queries).

To perform a single character wildcard search use the "?" symbol.

To perform a multiple character wildcard search use the "*" symbol.

The single character wildcard search looks for terms that match that with the single character replaced. For example, to search for "text" or "test" you can use the search:

    te?t

Multiple character wildcard searches looks for 0 or more characters. For example, to search for test, tests or tester, you can use the search:

    test*

You can also use the wildcard searches in the middle of a term.

    te*t

Note: You cannot use a * or ? symbol as the first character of a search.

#### Regular Expression Searches

Lucene supports regular expression searches matching a pattern between forward slashes "/". For example to find documents containing "moat" or "boat":

    /[mb]oat/

#### Fuzzy Searches

Lucene supports fuzzy searches based on Damerau-Levenshtein Distance. To do a fuzzy search use the tilde, "~", symbol at the end of a Single word Term. For example to search for a term similar in spelling to "roam" use the fuzzy search:

    roam~

This search will find terms like foam and roams.

An additional (optional) parameter can specify the maximum number of edits allowed. The value is between 0 and 2, For example:

    roam~1

The default that is used if the parameter is not given is 2 edit distances.

#### Proximity Searches

Lucene supports finding words are a within a specific distance away. To do a proximity search use the tilde, "~", symbol at the end of a Phrase. For example to search for a "apache" and "jakarta" within 10 words of each other in a document use the search:

    "jakarta apache"~10

#### Range Searches

Range Queries allow one to match documents whose field(s) values are between the lower and upper bound specified by the Range Query. Range Queries can be inclusive or exclusive of the upper and lower bounds. Sorting is done lexicographically.

    mod_date:[20020101 TO 20030101]

This will find documents whose mod_date fields have values between 20020101 and 20030101, inclusive. Note that Range Queries are not reserved for date fields. You could also use range queries with non-date fields:

    title:{Aida TO Carmen}

This will find all documents whose titles are between Aida and Carmen, but not including Aida and Carmen.

Inclusive range queries are denoted by square brackets. Exclusive range queries are denoted by curly brackets.

#### Boosting a Term

Lucene provides the relevance level of matching documents based on the terms found. To boost a term use the caret, "^", symbol with a boost factor (a number) at the end of the term you are searching. The higher the boost factor, the more relevant the term will be.

Boosting allows you to control the relevance of a document by boosting its term. For example, if you are searching for

    jakarta apache

and you want the term "jakarta" to be more relevant boost it using the ^ symbol along with the boost factor next to the term. You would type:

    jakarta^4 apache

This will make documents with the term jakarta appear more relevant. You can also boost Phrase Terms as in the example:

    "jakarta apache"^4 "Apache Lucene"

By default, the boost factor is 1. Although the boost factor must be positive, it can be less than 1 (e.g. 0.2).

### Boolean Operators

Boolean operators allow terms to be combined through logic operators. Lucene supports AND, "+", OR, NOT and "-" as Boolean operators (Note: Boolean operators must be ALL CAPS).

#### OR

The OR operator links two terms and finds a matching document if either of the terms exist in a document. This is equivalent to a union using sets. The symbol || can be used in place of the word OR.

To search for documents that contain either "jakarta apache" or just "jakarta" use the query:

    "jakarta apache" jakarta

or

    "jakarta apache" OR jakarta

#### AND

The AND operator matches documents where both terms exist anywhere in the text of a single document. This is equivalent to an intersection using sets. The symbol && can be used in place of the word AND.

To search for documents that contain "jakarta apache" and "Apache Lucene" use the query:

    "jakarta apache" AND "Apache Lucene"

#### +

The "+" or required operator requires that the term after the "+" symbol exist somewhere in a the field of a single document.

To search for documents that must contain "jakarta" and may contain "lucene" use the query:

    +jakarta lucene

#### NOT

The NOT operator excludes documents that contain the term after NOT. This is equivalent to a difference using sets. The symbol ! can be used in place of the word NOT.

To search for documents that contain "jakarta apache" but not "Apache Lucene" use the query:

    "jakarta apache" NOT "Apache Lucene"

Note: The NOT operator cannot be used with just one term. For example, the following search will return no results:

    NOT "jakarta apache"

#### -

The "-" or prohibit operator excludes documents that contain the term after the "-" symbol.

To search for documents that contain "jakarta apache" but not "Apache Lucene" use the query:

    "jakarta apache" -"Apache Lucene"

### Grouping

Lucene supports using parentheses to group clauses to form sub queries. This can be very useful if you want to control the boolean logic for a query.

To search for either "jakarta" or "apache" and "website" use the query:

    (jakarta OR apache) AND website

This eliminates any confusion and makes sure you that website must exist and either term jakarta or apache may exist.

### Field Grouping

Lucene supports using parentheses to group multiple clauses to a single field.

To search for a title that contains both the word "return" and the phrase "pink panther" use the query:

    title:(+return +"pink panther")

### Escaping Special Characters

Lucene supports escaping special characters that are part of the query syntax. The current list special characters are

+ - && || ! ( ) { } [ ] ^ " ~ * ? : \ /

To escape these character use the \ before the character. For example to search for (1+1):2 use the query:

    \(1\+1\)\:2