tapply applies a function to each cell of a ragged array,
  that is to each (non-empty) group of values given by a unique
  combination of the levels of certain factors.  NOTE: This man page is for the tapply S4 generic function
  defined in the BiocGenerics package.
  See ?base::tapply for the default method
  (defined in the base package).
  Bioconductor packages can define specific methods for objects
  (typically list-like or vector-like) not supported by the
  default method.
tapply(X, INDEX, FUN=NULL, ..., simplify=TRUE)?base::tapply for the details.Specific methods can support other objects (typically list-like or vector-like). Please refer to the documentation of a particular method for the details.
X.
    See ?base::tapply for the details.Specific methods can support other objects (typically list-like). Please refer to the documentation of a particular method for the details.
?base::tapply for a description of
    these arguments.
  ?base::tapply for the value returned by the
  default method.Specific methods defined in Bioconductor packages should 
  behave as consistently as possible with the default method.
base::tapply for the default tapply
          method.
showMethods for displaying a summary of the
          methods defined for a given generic function.
selectMethod for getting the definition of
          a specific method.
tapply method (defined
          for Vector objects).
tapply  # note the dispatch on the 'X' and 'INDEX' args only
showMethods("tapply")
selectMethod("tapply", c("ANY", "ANY"))  # the default method
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