[Rd] 1.9.0-devel: _ in read.delim and make.names

[Barry Rowlingson]

Wolfram Fischer wrote:
> In R 1.9.0, make.names will accept "_" as a valid character
> for a syntactically valid name.
> 
> I would appreciate to have an option in ``read.delim'' (etc.)
> that would change "_" in headers of input files to "."
> for compatibility with code and data written for R 1.8.1 and before.
> 

  Given that you are going to have to change your code to invoke this 
parameter, you may as well just write a 'makeOldStyleNames' function and 
call that.

  For example, suppose you currently have:

  myData = read.table("data.csv",sep=",",head=T)
  print(myData$foo.1)

and the data file has a column 'foo_1' which has been renamed to foo.1.

If the option is added to read.table, you'll have to change your code to 
  something like:

  myData = read.table("data.csv", sep=",", head=T, oldNames=T)

Now that would break in pre-1.9.0 releases. However, if you do:

  myData = read.table("data.csv", sep=",", head=T)
  names(myData) = makeOldStyleNames(names(myData))

  then, as long as makeOldStyleNames doesn't do anything to old style 
(dotted) names, and works in 1.8 and 1.9, you have achieved your goal 
and got back-compatibility as well.

  The makeOldStyleNames could be quite tricky - just replacing '_' with 
'.' might break if you have 'foo_1' and 'foo.1' in your data frame.

Perhaps doing the replacement and then calling R's make.names() with 
'unique=T' will work - depending on what 1.9 does in make.unique.

Baz