MS Data Analysis

Description Usage Arguments Details Value Author(s) See Also Examples

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.

## 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"), ...)

`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.

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.

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

Johannes Rainer

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

## 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)))))