[R] Listing Variables

[Farrel Buchinsky]

How does one create a vector whose contents is the list of variables in a
dataframe pertaining to a particular pattern?
This is so simple but I cannot find a straightforward answer.
I want to be able to pass the contents of that list to a "for" loop.

So let us assume that one has a dataframe whose name is Data. And let us
assume one had the height of a group of people measured at various ages.

It could be made up of vectors Data$PersonalID, Data$FirstName,
Data$LastName, Data$Height.1, Data$Height.5, Data$Height.9,
Data$Height.10,Data$Height.12,Data$Height.20....many many more variables.

How would one create a vector of all the Height variable names.

The simple workaround is to not bother creating the vector "Data$Height.1"
"Data$Height.5" "Data$Height.9" "Data$Height.10"
"Data$Height.12""Data$Height.20"...but rather just to use the sapply
function. However with some functions the sapply will not work and it is
necessary to supply each variable name to a function (see thread at 
Repeating tdt function on thousands of variables)


This is such a core capability. I would like to see it in the R-Wiki but 
could not find it there.

-- 
Farrel Buchinsky, MD
Pediatric Otolaryngologist
Allegheny General Hospital
Pittsburgh, PA