
234 R Programming for Bioinformatics
Exercise 8.2
Use the function ppc from Exercise 2.16 to create a new function that can find
and return the probes that map to any chromosome (just prepend the caret
to the chromosome numb er) or the chromosome number with a p or a q after
it.
8.2.3 Efficient apply-like functions
While the apply family of functions provides a very useful abstraction and
a succinct notation, its generality precludes a truly efficient implementation.
For this reason there are other, more efficient functions, for tasks that are
often performed, provided in R and in some add-on packages. These include
rowSums, rowMeans, colSums and colMeans,