Access the raw data from an \code{mzR} object.


 header(object, scans, ...)

 peaksCount(object, scans, ...)

 \S4method{peaks}{mzRpwiz}(object, scans)
 \S4method{peaks}{mzRnetCDF}(object, scans)

 \S4method{spectra}{mzRpwiz}(object, scans)   ## same as peaks
 \S4method{spectra}{mzRnetCDF}(object, scans)

 get3Dmap(object, scans, lowMz, highMz, resMz, ...)

 \S4method{chromatogram}{mzRpwiz}(object, chrom)

 \S4method{chromatograms}{mzRpwiz}(object, chrom)  ## same as chromatogram

 \S4method{chromatogramHeader}{mzRpwiz}(object, chrom)

 tic(object, ...)




  \item{object}{An instantiated \code{mzR} object.}
  \item{scans}{A \code{numeric} specifying which scans to
    return. Optional for the \code{header}, \code{peaks}, \code{spectra}
    and \code{peaksCount} methods. If ommited, the requested data for
    all peaks is returned. }

  \item{lowMz, highMz}{\code{Numeric}s defining the m/z range to be
  \item{resMz}{a \code{numeric} defining the m/z resolution.}

    For \code{chromatogram}, \code{chromatograms} and
    \code{chromatogramHeader}: \code{numeric} specifying the index
    of the chromatograms to be extracted from the file. If omitted, data
    for all chromatograms is returned. 
  \item{...}{Other arguments. A \code{scan} parameter can be passed to
    \code{peaks}.}  }


  Access the MS raw data. The \code{peaks}, \code{spectra} (can be used
  interchangeably) and \code{peaksCount} functions return the (m/z,
  intensity) pairs and the number peaks in the
  spectrum/spectra. \code{peaks} and \code{spectra} return a single
  matrix if \code{scans} is a \code{numeric} of length 1 and a list of
  matrices if several scans are asked for or no \code{scans} argument is
  provided (i.e all spectra in the oject are retured). \code{peaksCount}
  will return a numeric of length \code{n}.
  The \code{\link{header}} function returns a \code{data.frame} containing
  \code{seqNum}, \code{acquisitionNum}, \code{msLevel},
  \code{peaksCount}, \code{totIonCurrent}, \code{retentionTime} (in
  seconds), \code{basePeakMZ}, \code{basePeakIntensity},
  \code{collisionEnergy}, \code{ionisationEnergy}, \code{lowM},
  \code{highMZ}, \code{precursorScanNum}, \code{precursorMZ},
  \code{precursorCharge}, \code{precursorIntensity},
  \code{mergedScan}, \code{mergedResultScanNum},
  \code{mergedResultStartScanNum}, \code{mergedResultEndScanNum},
  \code{filterString}, \code{spectrumId}, \code{centroided}
  (\code{logical} whether the data of the spectrum is in centroid mode
  or profile mode; only for pwiz backend), \code{injectionTime} (ion
  injection time, in milliseconds), \code{ionMobilityDriftTime} (in
  milliseconds), \code{isolationWindowTargetMZ},
  \code{isolationWindowUpperOffset}, \code{scanWindowLowerLimit} and
  \code{scanWindowUpperLimit}. If multiple scans are queried, a
  \code{data.frame} is returned with the scans reported along the
  rows. For missing or not defined spectrum variables \code{NA} is reported.

  The \code{get3Dmap} function performs a simple resampling between
  \code{lowMz} and \code{highMz} with \code{reMz} resolution. A matrix
  of dimensions \code{length(scans)} times
  \code{seq(lowMz,highMz,resMz)} is returned.

  The \code{chromatogram} (\code{chromatograms}) accessors return
  chromatograms for the MS file handle. If a single index is provided,
  as \code{data.frame} containing the retention time (1st columns) and
  intensities (2nd column) is returned. The name of the former is always
  \code{time}, while the latter will depend on the run parameters.

  If more than 1 or no chromatogram indices are provided, then a list of
  chromatograms is returned; either those passed as argument or all of
  them. By default, the first (and possibly only) chromatogram is the
  total ion count, which can also be accessed with the \code{tic}

  The \code{nChrom} function returns the number of chromatograms,
  including the total ion chromatogram.

  The \code{chromatogramHeader} returns (similar to the \code{header}
  function for spectra) a \code{data.frame} with metadata information
  for the individual chromatograms. The \code{data.frame} has the
  columns: \code{"chromatogramId"} (the ID of the chromatogram as
  specified in the file), \code{"chromatogramIndex"} (the index of the
  chromatogram within the file), \code{"polarity"} (the polarity for the
  chromatogram, 0 for negative, +1 for positive and -1 for not set),
  \code{"precursorIsolationWindowTargetMZ"} (the isolation window m/z of
  the precursor), \code{"precursorIsolationWindowLowerOffset"},
  \code{"precursorIsolationWindowUpperOffset"} (lower and upper offset
  for the isolation window m/z), \code{"precursorCollisionEnergy"}
  (collision energy),
  \code{"productIsolationWindowLowerOffset"} and
  \code{"productIsolationWindowUpperOffset"} (definition of the m/z
  isolation window for the product).
  Note that access to chromatograms is only supported in the \code{pwiz}

  The column \code{acquisitionNum} in the \code{data.frame} returned by
  the \code{header} method contains the index during the scan in which
  the signal from the spectrum was measured. The \code{pwiz} backend
  extracts this number from the spectrum's ID provided in the mzML
  file. In contrast, column \code{seqNum} contains the index of each
  spectrum within the file and is thus consecutively numbered. Spectra
  from files with multiple MS levels are linked to each other \emph{via}
  their \code{acquisitionNum}: column \code{precursorScanNum} of an e.g. MS
  level 2 spectrum contains the \code{acquisitionNum} of the related MS
  level 1 spectrum.

  Spectrum identifiers are only specified in \emph{mzML} files, thus,
  for all other file types the column \code{"spectrumId"} of the result
  \code{data.frame} returned by \code{header} contains \code{"scan="}
  followed by the acquisition number of the spectrum. Also, only the
  \code{pwiz} backend supports extraction of the spectras' IDs from
  \emph{mzML} files. Thus, only \emph{mzML} files read with
  \code{backend = "pwiz"} provide the spectrum IDs defined in the file. 
  The content of the spectrum identifier depends on the vendor and the 
  instrument acquisition settings and is reported here as a character, 
  in its raw form, without further parsing.

  \code{\link{instrumentInfo}} for metadata access and the
  \code{"\linkS4class{mzR}"} class.

  \code{\link{writeMSData}} and \code{\link{copyWriteMSData}} for
  functions to write MS data in \emph{mzML} or \code{mzXML} format.

  Steffen Neumann and Laurent Gatto

 filepath <- system.file("microtofq", package = "msdata")
 file <- list.files(filepath, pattern="MM14.mzML",
                     full.names=TRUE, recursive = TRUE)
 mz <- openMSfile(file)

 ## A shotgun LCMSMS experiment
 f <- proteomics(full.names = TRUE,
                 pattern = "TMT_Erwinia_1uLSike_Top10HCD_isol2_45stepped_60min_01.mzML.gz")
 x <- openMSfile(f, backend = "pwiz")
 head(chromatogram(x, 1L)) ## same as tic(x)
 str(chromatogram(x)) ## as a list

 p <- peaks(x) ## extract all peak information
 head(peaks(x, scan=4)) ## extract just peaks from the 4th scan

 ## An MRM experiment
 f <- proteomics(full.names = TRUE, pattern = "MRM")
 x <- openMSfile(f, backend = "pwiz")
 head(chromatogram(x, 1L)) ## same as tic(x)
 str(chromatogram(x, 10:12))  

 ## get the header information for the chromatograms
 ch <- chromatogramHeader(x)