plotChromPeakDensity: Plot chromatographic peak density along the retention time...

In xiaodfeng/DynamicXCMS: LC-MS and GC-MS Data Analysis

Plot chromatographic peak density along the retention time axis

Description

Plot the density of chromatographic peaks along the retention time axis and indicate which peaks would be (or were) grouped into the same feature based using the peak density correspondence method. Settings for the peak density method can be passed with an PeakDensityParam object to parameter param. If the object contains correspondence results and the correspondence was performed with the peak groups method, the results from that correspondence can be visualized setting simulate = FALSE.

Usage

## S4 method for signature 'XCMSnExp'
plotChromPeakDensity(object, mz, rt, param,
  simulate = TRUE, col = "#00000080", xlab = "retention time",
  ylab = "sample", xlim = range(rt), main = NULL, type = c("any",
  "within", "apex_within"), ...)

Arguments

object	A XCMSnExp object with identified chromatographic peaks.
mz	numeric(2) defining an mz range for which the peak density should be plotted.
rt	numeric(2) defining an optional rt range for which the peak density should be plotted. Defaults to the absolute retention time range of object.
param	PeakDensityParam from which parameters for the peak density correspondence algorithm can be extracted. If not provided and if object contains feature definitions with the correspondence/ peak grouping being performed by the peak density method, the corresponding parameter class stored in object is used.
simulate	logical(1) defining whether correspondence should be simulated within the specified m/z / rt region or (with simulate = FALSE) whether the results from an already performed correspondence should be shown.
col	Color to be used for the individual samples. Length has to be 1 or equal to the number of samples in object.
xlab	character(1) with the label for the x-axis.
ylab	character(1) with the label for the y-axis.
xlim	numeric(2) representing the limits for the x-axis. Defaults to the range of the rt parameter.
main	character(1) defining the title of the plot. By default (for main = NULL) the mz-range is used.
type	character(1) specifying how peaks are called to be located within the region defined by mz and rt. Can be one of "any", "within", and "apex_within" for all peaks that are even partially overlapping the region, peaks that are completely within the region, and peaks for which the apex is within the region. This parameter is passed to the chromPeaks function. See related documentation for more information and examples.
...	Additional parameters to be passed to the plot function. Data point specific parameters such as bg or pch have to be of length 1 or equal to the number of samples.

Details

The plotChromPeakDensity function allows to evaluate different settings for the peak density on an mz slice of interest (e.g. containing chromatographic peaks corresponding to a known metabolite). The plot shows the individual peaks that were detected within the specified mz slice at their retention time (x-axis) and sample in which they were detected (y-axis). The density function is plotted as a black line. Parameters for the density function are taken from the param object. Grey rectangles indicate which chromatographic peaks would be grouped into a feature by the peak density correspondence method. Parameters for the algorithm are also taken from param. See groupChromPeaks-density() for more information about the algorithm and its supported settings.

Value

The function is called for its side effect, i.e. to create a plot.

Author(s)

Johannes Rainer

See Also

groupChromPeaks-density() for details on the peak density correspondence method and supported settings.

Examples

## Below we perform first a peak detection (using the centWave
## method) on some of the test files from the faahKO package.
library(faahKO)
library(xcms)
fls <- dir(system.file("cdf/KO", package = "faahKO"), recursive = TRUE,
           full.names = TRUE)

## Reading 2 of the KO samples
raw_data <- readMSData(fls[1:2], mode = "onDisk")

## Perform the peak detection using the centWave method (settings are tuned
## to speed up example execution)
res <- findChromPeaks(raw_data, param = CentWaveParam(noise = 3000, snthresh = 40))

## Align the samples using obiwarp
res <- adjustRtime(res, param = ObiwarpParam())

## Plot the chromatographic peak density for a specific mz range to evaluate
## different peak density correspondence settings.
mzr <- c(305.05, 305.15)

plotChromPeakDensity(res, mz = mzr, pch = 16,
    param = PeakDensityParam(sampleGroups = rep(1, length(fileNames(res)))))

## Use a larger bandwidth
plotChromPeakDensity(res, mz = mzr, param = PeakDensityParam(bw = 60,
    sampleGroups = rep(1, length(fileNames(res)))), pch = 16)
## Neighboring peaks are now fused into one.

## Require the chromatographic peak to be present in all samples of a group
plotChromPeakDensity(res, mz = mzr, pch = 16,
    param = PeakDensityParam(minFraction = 1,
    sampleGroups = rep(1, length(fileNames(res)))))

xiaodfeng/DynamicXCMS documentation built on Aug. 6, 2023, 3:02 p.m.