Simplify and By Convert Factors To Numeric Values

Good day,

It's not described anywhere in the help page, but tapply and by 
functions will, by default, convert factors into numeric values. Perhaps 
this needs to be documented or the behaviour changed.

It *is* described in the help page.

This returns a list of objects and each object class has "factor"

tapply(rep(1:2,2), rep(1:2,2),
   function(x) factor(LETTERS[x], levels = LETTERS))

and this

tapply(1:3, 1:3, function(x) factor(LETTERS[x], levels = LETTERS))

1 2 3
1 2 3

returns a vector object with no class.

The documentation states "... tapply returns a multi-way array 
containing the values ..." but doesn't mention anything about converting 
factors into integers. I'd expect the values to be of the same type.

and also states

"If FUN returns a single atomic value for each such cell ... and when 
simplify is TRUE ...  if the return value has a class (e.g., an object of 
class "Date") the class is discarded."

which is what just happened in your example.

Maybe you want:

unlist(tapply(1:3, 1:3, function(x) factor(LETTERS[x],
   levels = LETTERS),simplify=FALSE))

Trying to preserve class worked here in a way you might have 
hoped/expected, but might lead to difficulties in other uses.

HTH,

Chuck