runGC {metaMS} | R Documentation

## Wrapper for processing of GC-MS data files

### Description

Main function of the pipeline for GC-MS data processing. It includes XCMS peak detection, definition of pseudospectra, and compound identification by comparison to a database of standards. The function also takes care of removal of artefacts like column bleeding and plasticizers, and definition of unknowns, consistently present across samples.

### Usage

    runGC(files, xset, settings, rtrange = NULL, DB = NULL,
          removeArtefacts = TRUE, findUnknowns = nexp >= mcs,
          returnXset = FALSE, RIstandards = NULL, nSlaves = 0)

### Arguments

`files` | input files, given as a vector of strings containing the complete paths. All formats supported by XCMS can be used.
`xset` | alternatively, one can present a list of xcmsSet objects for whom CAMERA grouping has been done. In this case, only the annotation process will be done. If both `files` and `xset` are given, the former takes precedence.
`settings` | a nested list of settings, to be used at individual steps of the pipeline.
`rtrange` | part of the chromatograms that is to be analysed. If given, it should be a vector of two numbers indicating minimal and maximal retention time (in minutes).
`DB` | database containing the spectra of the pure standards. At least the following fields should be present: `Name`, `std.rt`, `pspectrum` and `monoMW`.
`removeArtefacts` | logical, whether or not to remove patterns identified as (e.g.) column bleeding. Only performed if a database containing such patterns is available.
`findUnknowns` | logical, whether to find patterns without identification that are present consistently in several samples. The default is to use TRUE if the number of samples is larger than the min.class.size setting in the 'betweenSamples' metaSetting.
`returnXset` | logical: should the XCMS output be returned? If yes, this is a a list of `xcmsSet` objects, one element for each input file.
`RIstandards` | A two-column matrix containing for the standards defining the RI scale both retention times and retention indices. If not given, no RI values will be calculated and retention times will be used instead.
`nSlaves` | Number of cores to be used in peak picking.

### Value

A list with the following elements:

`PeakTable` | data.frame containing annotation information. Every line is a feature, i.e. a pseudospectrum. The first columns are used to give information about these features, a.o. compound name, CAS and Chemspider IDs, etcetera. The last of these meta-information columns is always the one giving the retention time: “rt”. After that, columns correspond to input files, and give measures of intensities for every single one of the features. If a feature is not detected in a sample, this is indicated with “0” (zero).
`PseudoSpecra` | A list of pseudospectra in msp format, in the same order as the rows in the PeakTable.
`xset` | optionally, the xcmsSet object is returned, which can be useful for more detailed inspection of the results. It can also be used as an input for `runGC`, e.g., to test different annotation settings independently of the xcms/CAMERA part.
`sessionInfo` | The output of `sessionInfo()` to keep track of the sw version used for the processing

### Author(s)

Ron Wehrens

### References

R. Wehrens, G. Weingart and F. Mattivi: "An open-source pipeline for GC-MS-based untargeted metabolomics". Submitted.

### See Also

`msp`, `treat.DB`, `runCAMERA`, `peakDetection`, `matchSamples2DB`, `matchSamples2Samples`, `getAnnotationMat`, `addRI`

### Examples

    ## analysis of an xset object
    data(threeStdsDB)
    data(FEMsettings)

    data(GCresults) ## pre-compiled results
    names(GCresults)

    ## Not run:
    if (require(metaMSdata)) {
      ## object GCresults is created by
      cdfdir <- system.file("extdata", package = "metaMSdata")
      cdffiles <- list.files(cdfdir, pattern = "_GC_",
                             full.names = TRUE, ignore.case = TRUE)
      GCresults <- runGC(files = cdffiles, settings = TSQXLS.GC, DB = DB,
                         returnXset = TRUE)

      ## to start directly from the XCMS/CAMERA results and not include
      ## peak picking in the pipeline, simply provide the "xset" argument
      ## rather than the "files" argument.

      ## no annotation database
      result.noannot <- runGC(xset = GCresults$xset, settings = TSQXLS.GC)
      }

    ## End(Not run)

[Package metaMS version 1.20.0 Index]