R: SolrQuery

SolrQuery-class {rsolr}

R Documentation

SolrQuery

Description

The SolrQuery object represents a query to be sent to a SolrCore. This is a low-level interface to query construction but will not be useful to most users. The typical reason to directly manipulate a query would be to batch more operations than is possible with the high-level SolrFrame, e.g., combining multiple aggregations.

Details

A SolrQuery API borrows many of the same verbs from the base R API, including subset, transform, sort, xtabs, head, tail, rev, etc.

The typical workflow is to construct a query, perform various manipulations, and finally retrieve a result by passing the query to a SolrCore, typically via the docs or facets functions.

Accessors

params(x), params(x) <- value: Gets/sets the parameters of the query, which roughly correspond to the parameters of a Solr “select” request. The only reason to manipulate the underlying query parameters is to either initiate a headache or to do something really tricky with Solr, which implies the former.

Querying

subset(x, subset, select, fields, select.from = character()): Behaves like the base subset, with some extensions. The fields argument is exclusive with select, and should be a character vector of field names, potentially with wildcards. The select.from argument gives the names that are filtered by select, since SolrQuery is not associated with any SolrCore, and thus does not know the field set (in the future, we might use laziness to avoid this problem).
searchDocs(x, q): Performs a conventional document search using the query string q. The main difference to filtering (subset) is that (by default) Solr will order the result by score, i.e., how well each document matches the query.

Constructor

SolrQuery(expr): Constructs a new SolrQuery instance. If expr is non-missing, it is passed to subset and thus serves as an initial restriction.

Faceting

The Solr facet component counts documents and calculates statistics on a group-wise basis.

facet(x, by, ..., useNA=FALSE, sort=NULL, decreasing=FALSE, limit=NA_integer_): Returns a query that will compute the number of documents in each group, where the grouping is given as by, typically a formula, or NULL for global aggregation. Arguments in ... are quoted and should be expressions that summarize fields, or mathematical combinations of fields. The names of the statistics are taken from the argument names; if a name is omitted, a best guess is made from the expression. If useNA is TRUE, statistics and counts are computed for the bin where documents have a missing value for one the grouping variables. If sort is non-NULL, it should name a statistic by which the results should be sorted. This is mostly useful in conjunction if a limit is specified, so that only the top-N statistics are returned.

The formula should consist of Solr field names, or calls that evaluate to logical and refer to one or more Solr fields. If the latter, the results are grouped by TRUE, FALSE and (optionally) NA for that term. As a special case, a term can be a call to cut on any numeric or date field, which will group by bin.

Grouping

The Solr grouping component causes results to be returned nested into groups. The main use case would be to restrict to the first or last N documents in each group. This functionality is not related to aggregation; see facet.

group(x, by, limit = .Machine$integer.max, offset = 0L, env = emptyenv()): Returns the grouping of x according to by, which might be a formula, or an expression that evaluates (within env) to a factor. The current sort specification applies within the groups, and any subsequent sorting applies to the groups themselves, by using the maximum value within the each group. Only the top limit documents, starting after the first offset, are returned from each group. Restricting that limit is probably the main reason to use this functionality.

Coercion

These two functions are very low-level; users should almost never need to call these.

translate(x, target, core): Translates the query x into the language of Solr, where core specifies the destination SolrCore. The target argument should be missing.
as.character(x): Converts the query into a string to be sent to Solr. Remember to translate first, if necessary.

Author(s)

Michael Lawrence