selectInBatches {ChemmineR} | R Documentation

## Select in Batches

### Description

When doing a select were the condition is a large number of ids it is not always possible to include them in a single SQL statement. This function will break the list of ids into chunks and send the query for each batch. The resutls are appended and returned as one data frame.

### Usage

    selectInBatches(conn, allIndices, genQuery, batchSize = 1e+05)

### Arguments

`conn` | Database connection object
`allIndices` | A vector of indices to pass to the genQuery function in batches.
`genQuery` | A function which takes a vector of indices and constructs an SQL SELECT statement returning records for the given indicies.
`batchSize` | How many indicies to put in each batch.

### Value

A data frame with the results of the query as if all inidices had been included in a single SELEcT statement.

### Author(s)

Kevin Horan

### Examples

    ##---- Should be DIRECTLY executable !! ----
    ##-- ==>  Define data, use random,
    ##--	or do  help(data=index)  for the standard data sets.

    ## The function is currently defined as
    function (conn, allIndices, genQuery, batchSize = 1e+05)
    {
        batchByIndex(allIndices, function(indexBatch) {
            df = dbGetQuery(conn, genQuery(indexBatch))
            result = rbind(result, df)
        }, batchSize)
        result
      }

[Package ChemmineR version 3.36.0 Index]