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Base MsBackend class providing data caching mechanism

Source: R/MsBackendCached.R
MsBackendCached.Rd

The MsBackendCached class is a rudimentary implementation of the MsBackend providing a simple mechanism to cache spectra data locally. This class is thought to be used as a base class for other MsBackend implementations to reuse its caching mechanism and avoid having to re-implement commonly used methods. This class is thus not thought to be used directly by a user.

The MsBackendCached caching mechanism allows MsBackend instances to add or replace spectra variables even if the backend used by them does not allow to alter values (e.g. if a SQL database is used as a backend). Any replacement operation with $<- will add the specified values to a local data.frame within the MsBackendCached class that allows to cache these values (increasing obviously the memory demand of the object).

Any data accessor functions of the extending MsBackend class (such as $ or msLevel() or spectraData()) should first use callNextMethod() to call the respective accessor of MsBackendCached that will evaluate if the requested spectra variable(s) are in the local cache and return these. If the requested spectra variables are neither in the local cache, nor listed in the @spectraVariables slot (which defines all spectra variables that can be requested from the extending MsBackend class) but are core spectra variables then missing values of the correct data type are returned.

Usage

MsBackendCached()

# S4 method for class 'MsBackendCached'
backendInitialize(
  object,
  data = data.frame(),
  nspectra = 0L,
  spectraVariables = character(),
  ...
)

# S4 method for class 'MsBackendCached'
dataStorage(object)

# S4 method for class 'MsBackendCached,ANY'
extractByIndex(object, i)

# S4 method for class 'MsBackendCached'
length(x)

# S4 method for class 'MsBackendCached'
spectraVariables(object)

# S4 method for class 'MsBackendCached'
spectraData(object, columns = spectraVariables(object))

# S4 method for class 'MsBackendCached'
spectraData(object) <- value

# S4 method for class 'MsBackendCached'
x[i, j, ..., drop = FALSE]

# S4 method for class 'MsBackendCached'
x$name

# S4 method for class 'MsBackendCached'
x$name <- value

# S4 method for class 'MsBackendCached'
selectSpectraVariables(object, spectraVariables = spectraVariables(object))

# S4 method for class 'MsBackendCached'
show(object)

# S4 method for class 'MsBackendCached'
intensity(object)

# S4 method for class 'MsBackendCached'
ionCount(object)

# S4 method for class 'MsBackendCached'
mz(object)

Arguments

object

A MsBackendCached object.

data

For backendInitialize(): (optional) data.frame with cached values. The number of rows (and their order) has to match the number of spectra.

nspectra

For backendInitialize(): integer with the number of spectra.

spectraVariables

For backendInitialize(): character with the names of the spectra variables that are provided by the extending backend. For selectSpectraVariables(): character specifying the spectra variables to keep.

...

ignored

i

For [: integer with the indices to subset the object.

x

A MsBackendCached object.

columns

For spectraData(): character with the names of the spectra variables to retrieve.

value

replacement value for <- methods. See individual method description or expected data type.

j

For [: ignored.

drop

For [: not considered.

name

For $<-: the name of the spectra variable to set.

Value

See documentation of respective function.

Implementation notes

Classes extending the MsBackendCached need to

  • call the backendInitialize() method of this class in their own backendInitialize() method and set at least the number of spectra with the nspectra parameter and the spectraVariables that are available to the (extending) backend class.

  • implement the spectraData() method that also calls the spectraData() method from MsBackendCached to also retrieve cached values (e.g. using res <- callNextMethod() at the beginning of the spectraData function). The spectraData,MsBackendCached method will return NULL if the selected spectra variables were not cached and are not core spectra variables not being provided by the extending backend. Thus, the extending backend can then proceed to retrieve the respective values from its own backend/data storage.

  • implement eventually the [ method that calls in addition the [ from the MsBackendCached.

All other methods accessing or setting spectra variables don't need to be implemented by the extending backend class (the default implementations of the MsBackendCached will then be used instead; these ensure that cached values are returned first). Spectra variables can be modified or added using the $<- method of the MsBackendCached. Replacing or adding multiple variables using the spectraData<- is not supported by MsBackendCached. The extending backend might however implement such a method that internally uses $<- to add/replace single variables.

The MsBackendCached has the following slots:

  • nspectra: integer(1) defining the number of spectra of the backend. This variable needs to be set and must match the number of rows of localData and the actual number of spectra in the (extending) backend.

  • localData: data.frame with the cached local data. Any replacement operation with $<- will set/add a column with the respective values.

  • spectraVariables: character defining the spectra variables that are provided by the extending MsBackend class (e.g. all spectra variables that can be retrieved from the data base or original data files).

Available methods

  • acquisitionNum(): returns the acquisition number of each spectrum. Returns an integer of length equal to the number of spectra (with NA_integer_ if not available).

  • backendInitialize(): initializes the backend. The method takes parameters data (data.frame with cached data), nspectra (integer defining the number of spectra) and spectraVariables (character with the spectra variables that are provided by the extending backend.

  • centroided(), centroided<-: gets or sets the centroiding information of the spectra. centroided returns a logical vector of length equal to the number of spectra with TRUE if a spectrum is centroided, FALSE if it is in profile mode and NA if it is undefined. See also isCentroided for estimating from the spectrum data whether the spectrum is centroided. value for centroided<- is either a single logical or a logical of length equal to the number of spectra in object.

  • collisionEnergy(), collisionEnergy<-: gets or sets the collision energy for all spectra in object. collisionEnergy() returns a numeric with length equal to the number of spectra (NA_real_ if not present/defined), collisionEnergy<- takes a numeric of length equal to the number of spectra in object.

  • dataOrigin(): gets a character of length equal to the number of spectra in object with the data origin of each spectrum. This could e.g. be the mzML file from which the data was read.

  • intensity(): gets the intensity values from the spectra. Returns a IRanges::NumericList() of numeric vectors (intensity values for each spectrum). The length of the list is equal to the number of spectra in object.

  • ionCount(): returns a numeric with the sum of intensities for each spectrum. If the spectrum is empty (see isEmpty()), NA_real_ is returned.

  • isEmpty(): checks whether a spectrum in object is empty (i.e. does not contain any peaks). Returns a logical vector of length equal number of spectra.

  • isolationWindowLowerMz(), isolationWindowLowerMz<-: gets or sets the lower m/z boundary of the isolation window.

  • isolationWindowTargetMz(), isolationWindowTargetMz<-: gets or sets the target m/z of the isolation window.

  • isolationWindowUpperMz(), isolationWindowUpperMz<-: gets or sets the upper m/z boundary of the isolation window.

  • length(): returns the number of spectra (i.e. the @nspectra).

  • lengths(): gets the number of peaks (m/z-intensity values) per spectrum. Returns an integer vector (length equal to the number of spectra). For empty spectra, 0 is returned.

  • msLevel(): gets the spectra's MS level. Returns an integer vector (of length equal to the number of spectra) with the MS level for each spectrum (or NA_integer_ if not available).

  • mz(): gets the mass-to-charge ratios (m/z) from the spectra. Returns a IRanges::NumericList() or length equal to the number of spectra, each element a numeric vector with the m/z values of one spectrum.

  • polarity(), polarity<-: gets or sets the polarity for each spectrum. polarity returns an integer vector (length equal to the number of spectra), with 0 and 1 representing negative and positive polarities, respectively. polarity<- expects an integer vector of length 1 or equal to the number of spectra.

  • precursorCharge(), precursorIntensity(), precursorMz(), precScanNum(), precAcquisitionNum(): get the charge (integer), intensity (numeric), m/z (numeric), scan index (integer) and acquisition number (interger) of the precursor for MS level 2 and above spectra from the object. Returns a vector of length equal to the number of spectra in object. NA are reported for MS1 spectra of if no precursor information is available.

  • rtime(), rtime<-: gets or sets the retention times for each spectrum (in seconds). rtime() returns a numeric vector (length equal to the number of spectra) with the retention time for each spectrum. rtime<- expects a numeric vector with length equal to the number of spectra.

  • scanIndex(): returns an integer vector with the scan index for each spectrum. This represents the relative index of the spectrum within each file. Note that this can be different to the acquisitionNum() of the spectrum which is the index of the spectrum as reported in the mzML file.

  • selectSpectraVariables(): subset the object to specified spectra variables. This will eventually remove spectra variables listed in @spectraVariables and will also drop columns from the local cache if not among spectraVariables.

  • smoothed(),smoothed<-: gets or sets whether a spectrum is smoothed. smoothed() returns a logical vector of length equal to the number of spectra. smoothed<- takes a logical vector of length 1 or equal to the number of spectra in object.

  • spectraVariables(): returns the available spectra variables, i.e. the unique set of core spectra variables, cached spectra variables and spectra variables defined in the @spectraVariables slot (i.e. spectra variables thought to be provided by the extending MsBackend instance).

  • spectraData(): returns a DataFrame with cached spectra variablers or initialized core spectra variables. Parameter spectraVariables allows to specify the variables to retrieve. The function returns NULL if the requested variables are not cached and are not provided by the extending backend. Note that this method only returns cached spectra variables or core spectra variables not provided by the extending backend. It is the responsibility of the extending backend to add/provide these.

  • [: subsets the cached data. Parameter i needs to be an integer vector.

  • $, $<-: access or set/add a single spectrum variable (column) in the backend.

See also

MsBackend for the documentation of MS backends.

Author

Johannes Rainer