batchByIndex {ChemmineR} | R Documentation

## Batch by Index

### 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 allow the indexProcessor to deal with just a small number of ids.

### Usage

    batchByIndex(allIndices, indexProcessor, batchSize = 1e+05)

### Arguments

`allIndices` | A vector of values that will be broken into batches and passed as an argument to the `indexProcessor` function.
`indexProcessor` | A function that takes one batch if indices. It is called once for each batch. The return value from this function is ignored. To accumulate results you can write to a global variable using the "<<-" operator.
`batchSize` | The size of each batch. The last batch may be smaller than this value.

### Value

No value is returned.

### Author(s)

Kevin Horan

### See Also

`parBatchByIndex`

### Examples

    	## Not run:
    		result=NA
    		indices = 1:10000

    		#run a query on each batch of indexes, appending each result to
    		# "result" as we go.
    		batchByIndex(indices, function(indexBatch){
    				df = dbGetQuery(dbConnection, generateQuery(indexBatch))
    				result <<- if(is.na(result)) df else  rbind(result,df)
    		},1000)

    ## End(Not run)

[Package ChemmineR version 3.42.2 Index]