Chromatogram-class {MSnbase} | R Documentation

## Representation of chromatographic MS data

### Description

The `Chromatogram` class is designed to store chromatographic MS data, i.e. pairs of retention time and intensity values. Instances of the class can be created with the `Chromatogram` constructor function but in most cases the dedicated methods for `OnDiskMSnExp` and `MSnExp` objects extracting chromatograms should be used instead (i.e. the `chromatogram` method).

`Chromatogram`: create an instance of the `Chromatogram` class.

`aggregationFun,aggregationFun<-` get or set the aggregation function.

`rtime` returns the retention times for the rentention time - intensity pairs stored in the chromatogram.

`intensity` returns the intensity for the rentention time - intensity pairs stored in the chromatogram.

`mz` get the mz (range) of the chromatogram. The function returns a `numeric(2)` with the lower and upper mz value.

`precursorMz` get the mz of the precursor ion. The function returns a `numeric(2)` with the lower and upper mz value.

`fromFile` returns the value from the `fromFile` slot.

`length` returns the length (number of retention time - intensity pairs) of the chromatogram.

`as.data.frame` returns the `rtime` and `intensity` values from the object as `data.frame`.

`filterRt`: filters the chromatogram based on the provided retention time range.

`clean`: Removes unused 0-intensity data points. See `clean` documentation for more details and examples.

`plot`: plots a `Chromatogram` object.

`msLevel` returns the MS level of the chromatogram.

`isEmpty` returns `TRUE` for empty chromatogram or chromatograms with all intensities being `NA`.

`productMz` get the mz of the product chromatogram/ion. The function returns a `numeric(2)` with the lower and upper mz value.

`bin` aggregates intensity values from a chromatogram in discrete bins along the retention time axis and returns a `Chromatogram` object with the retention time representing the mid-point of the bins and the intensity the binned signal.

### Usage

    Chromatogram(rtime = numeric(), intensity = numeric(),
      mz = c(NA_real_, NA_real_), filterMz = c(NA_real_, NA_real_),
      precursorMz = c(NA_real_, NA_real_), productMz = c(NA_real_,
      NA_real_), fromFile = integer(), aggregationFun = character(),
      msLevel = 1L)

    aggregationFun(object)

    ## S4 method for signature 'Chromatogram'
    show(object)

    ## S4 method for signature 'Chromatogram'
    rtime(object)

    ## S4 method for signature 'Chromatogram'
    intensity(object)

    ## S4 method for signature 'Chromatogram'
    mz(object, filter = FALSE)

    ## S4 method for signature 'Chromatogram'
    precursorMz(object)

    ## S4 method for signature 'Chromatogram'
    fromFile(object)

    ## S4 method for signature 'Chromatogram'
    length(x)

    ## S4 method for signature 'Chromatogram'
    as.data.frame(x)

    ## S4 method for signature 'Chromatogram'
    filterRt(object, rt)

    ## S4 method for signature 'Chromatogram'
    clean(object, all = FALSE, na.rm = FALSE)

    ## S4 method for signature 'Chromatogram,ANY'
    plot(x, col = "#00000060", lty = 1,
      type = "l", xlab = "retention time", ylab = "intensity",
      main = NULL, ...)

    ## S4 method for signature 'Chromatogram'
    msLevel(object)

    ## S4 method for signature 'Chromatogram'
    isEmpty(x)

    ## S4 method for signature 'Chromatogram'
    productMz(object)

    ## S4 method for signature 'Chromatogram'
    bin(object, binSize = 0.5,
      breaks = seq(floor(min(rtime(object))), ceiling(max(rtime(object))), by
      = binSize), fun = max)

### Arguments

`rtime` | `numeric` with the retention times (length has to be equal to the length of `intensity`).
`intensity` | `numeric` with the intensity values (length has to be equal to the length of `rtime`).
`mz` | `numeric(2)` representing the mz value range (min, max) on which the chromatogram was created. This is supposed to contain the real range of mz values in contrast to the `filterMz` below. If not applicable use `mzrange = c(0, 0)`.
`filterMz` | `numeric(2)` representing the mz value range (min, max) that was used to filter the original object on mz dimension. If not applicable use `filterMz = c(0, 0)`.
`precursorMz` | `numeric(2)` for SRM/MRM transitions. Represents the mz of the precursor ion. See details for more information.
`productMz` | `numeric(2)` for SRM/MRM transitions. Represents the mz of the product. See details for more information.
`fromFile` | `integer(1)` the index of the file within the `OnDiskMSnExp` or `MSnExp` from which the chromatogram was extracted.
`aggregationFun` | `character` string specifying the function that was used to aggregate intensity values for the same retention time across the mz range. Supported are `"sum"` (total ion chromatogram), `"max"` (base peak chromatogram), `"min"` and `"mean"`.
`msLevel` | `integer` with the MS level from which the chromatogram was extracted.
`object` | A `Chromatogram` object.
`filter` | For `mz`: whether the mz range used to filter the original object should be returned (`filter = TRUE`), or the mz range calculated on the real data (`filter = FALSE`).
`x` | For `as.data.frame` and `length`: a `Chromatogram` object.
`rt` | For `filterRt`: `numeric(2)` defining the lower and upper retention time for the filtering.
`all` | For `clean`: `logical(1)` whether all 0 intensities should be removed (default is `FALSE`). See `clean` for more details and examples.
`na.rm` | For `clean`: `logical(1)` whether all `NA` intensities should be removed before cleaning the `Chromatogram`. Defaults to `FALSE`. See `clean` for more details and examples.
`col` | For `plot`: the color to be used for plotting.
`lty` | For `plot`: the line type. See `plot` for more details.
`type` | For `plot`: the type of plot. See `plot` for more details.
`xlab` | For `plot`: the x-axis label.
`ylab` | For `plot`: the y-axis label.
`main` | For `plot`: the plot title. If not provided the mz range will be used as plot title.
`...` | For `plot`: additional arguments to be passed to the `plot` function.
`binSize` | for `bin`: `numeric(1)` with the size of the bins (in seconds).
`breaks` | for `bin`: `numeric` defining the bins. Usually not required as the function calculates the bins automatically based on `binSize`.
`fun` | for `bin`: function to be used to aggregate the intensity values falling within each bin.

### Details

The `mz`, `filterMz`, `precursorMz` and `productMz` are stored as a `numeric(2)` representing a range even if the chromatogram was generated for only a single ion (i.e. a single mz value). Using ranges for `mz` values allow this class to be used also for e.g. total ion chromatograms or base peak chromatograms.

The slots `precursorMz` and `productMz` allow to represent SRM (single reaction monitoring) and MRM (multiple SRM) chromatograms. As example, a `Chromatogram` for a SRM transition 273 -> 153 will have a `@precursorMz = c(273, 273)` and a `@productMz = c(153, 153)`.

### Slots

`.__classVersion__,rtime,intensity,mz,filterMz,precursorMz,productMz,fromFile,aggregationFun,msLevel`

  See corresponding parameter above.

### Author(s)

Johannes Rainer

### See Also

`Chromatograms` for combining `Chromatogram` in a two-dimensional matrix (rows being mz-rt ranges, columns samples). `chromatogram` for the method to extract chromatogram data from a `MSnExp` or `OnDiskMSnExp` object. `clean` for the method to clean a `Chromatogram` object.

### Examples

    ## Create a simple Chromatogram object.
    ints <- abs(rnorm(100, sd = 100))
    rts <- seq_len(length(ints))
    chr <- Chromatogram(rtime = rts, intensity = ints)
    chr

    ## Extract intensities
    intensity(chr)

    ## Extract retention times
    rtime(chr)

    ## Extract the mz range - is NA for the present example
    mz(chr)

    ## plot the Chromatogram
    plot(chr)

    ## Create a simple Chromatogram object based on random values.
    chr <- Chromatogram(intensity = abs(rnorm(1000, mean = 2000, sd = 200)),
            rtime = sort(abs(rnorm(1000, mean = 10, sd = 5))))
    chr

    ## Get the intensities
    head(intensity(chr))

    ## Get the retention time
    head(rtime(chr))

    ## What is the retention time range of the object?
    range(rtime(chr))

    ## Filter the chromatogram to keep only values between 4 and 10 seconds
    chr2 <- filterRt(chr, rt = c(4, 10))

    range(rtime(chr2))

[Package MSnbase version 2.10.1 Index]