scidb (version 1.0-1)

iquery: Simple SciDB query tool

Description

Issue SciDB queries and optionally return output in a data frame.

Usage

iquery(query, `return` = FALSE, afl = TRUE, iterative = FALSE, n = 1000, excludecol, ...)

Arguments

query

A SciDB query string (character). Separate multiple queries with semicolons.

return

Set to TRUE to return output. Otherwise don't return query output. Only available when afl=TRUE

afl

TRUE indicates query is in AFL form, FALSE indicates AQL.

iterative

Set to TRUE to return a result iterator. FALSE returns entire result at once.

n

Maximum number of rows to return when iterating through results.

excludecol

An optional numeric range of columns to exclude from iterative results (only applies when iterative=TRIE).

...

Options passed on to read.table used to parse results.

Value

• If return=TRUE, return the query result in data frame form (similar to the command-line -olcsv+ output option).

  If return=FALSE, return the query ID number.

  SciDB errors encountered during query processing are propagated to R and can be handled with normal R error handling mechanisms.

  Set itreative=TRUE to return a result iterator. Use the iterator nextElem function to iteratively return results, a maximum of n results at a time. See help in the iterators package for examples and options.

Details

The iquery function is a simple analog of the command-line SciDB iquery program.

Examples

iquery("list('instances')",return=TRUE)

# A simple example that iterates through results using foreach
# Build an array with 1 million numbers from zero to 1.
iquery("store(build(<x:double>[i=1:1000000,100000,0],i/1000000),X)")
# Apply a function and return result in an iterator:
i <- iquery("apply(X, y, sin(x))", return=TRUE, iterative=TRUE)

# Sum up x and y (and dimension i too)
library("foreach")
foreach(j=i, .combine=function(...)colSums(rbind(...)))
# Compare with the much faster equivalent inside SciDB:
iquery("aggregate(apply(X, y, sin(x)),sum(x),sum(y))", return=TRUE)