sdfStream {ChemmineR} | R Documentation

## Streaming through large SD files

### Description

Streaming function to compute descriptors for large SD Files without consuming much memory. In addition to descriptor values, it returns a line index that defines the positions of each molecule in the source SD File. This line index can be used by the `read.SDFindex` function to retrieve specific compounds of interest from large SD Files without reading the entire file into memory.

### Usage

    sdfStream(input, output, append=FALSE, fct, Nlines = 10000, startline=1, restartNlines=10000, silent = FALSE, ...)

### Arguments

`input` | file name of input SD file
`output` | file name of tabular descriptor file
`append` | if `append=FALSE`, a new output file will be created, if one with the same name exists it will be overwritten; whereas `append=TRUE` will appended to this file.
`fct` | Function to select descriptor sets; any combination of descriptors, supported by `ChemmineR`, can be chosen here, as long as they can be represented in tabular format.
`Nlines` | Number of lines to read from input SD File at a time; the memory consumption will be proportional to this value.
`startline` | For restarting sdfStream at specific line assigned to `startline` argument. If assigned `startline` value does not match the first line of a molecule in the SD file then it will be reset to the start position of the next molecule in the SD file.
`restartNlines` | Number of lines to parse when `startline > 1` in order to identify proper molecule start position. The default value of 10,000 is usually a good choice.
`silent` | if `silent=FALSE`, the processing status will be printed to the screen, while `silent=TRUE` suppresses this output.
`...` | Arguments to be passed to/from other methods.

### Details

...

### Value

Writes a descriptor matrix to a tabular file. The first and last line number (position index) of each molecule is specified in the first two columns of the tabular output file, respectively.

### Author(s)

Thomas Girke

### References

SDF format definition: http://www.symyx.com/downloads/public/ctfile/ctfile.jsp

### See Also

Import/export functions: `read.AP`, `read.SDFset`, `read.SDFstr`, `read.SDFstr`, `read.SDFset`, `write.SDFsplit`

### Examples

    ## Load sample data
    library(ChemmineR)
    data(sdfsample); sdfset <- sdfsample
    ## Not run: write.SDF(sdfset, "test.sdf")

    ## Define descriptor set in a simple function
    desc <- function(sdfset) {
            cbind(SDFID=sdfid(sdfset),
                  # datablock2ma(datablocklist=datablock(sdfset)),
                  MW=MW(sdfset),
                  groups(sdfset),
                  # AP=sdf2ap(sdfset, type="character"),
                  rings(sdfset, type="count", upper=6, arom=TRUE)
            )
    }

    ## Run sdfStream with desc function and write results to a file called 'matrix.xls'
    sdfStream(input="test.sdf", output="matrix.xls", append=FALSE, fct=desc, Nlines=1000)

    ## Same as before but starting in SD file at line number 950
    sdfStream(input="test.sdf", output="matrix.xls", append=FALSE, fct=desc, Nlines=1000, startline=950)

    ## Select molecules from SD File using line index from sdfStream
    indexDF <- read.delim("matrix.xls", row.names=1)[,1:4]
    indexDFsub <- indexDF[indexDF$MW < 400, ] # Selects molecules with MW < 400
    sdfset <- read.SDFindex(file="test.sdf", index=indexDFsub, type="SDFset")

    ## Write result directly to SD file without storing larger numbers of molecules in memory
    read.SDFindex(file="test.sdf", index=indexDFsub, type="file", outfile="sub.sdf")

    ## Read atom pair string representation from file into APset
    apset <- read.AP(file="matrix.xls", colid="AP")
    cid(apsdf) <- as.character(indexDF$SDFID)

    ## End(Not run)

[Package ChemmineR version 3.32.1 Index]