R help - Mar 2008 - Replace values in data.frame conditional on another data.frame

Dear List,

I am looking for an efficient method for replacing values in a
data.frame conditional on the values of a separate data.frame. Here is
my scenario:
I have a data.frame (A) with say 1000 columns, and 365 rows. Each cell
in the data.frame has either valid value, or NA. I have an additional
data.frame (B) with the same number of rows and columns, with valid
values in all cells. What I would like to do, is replace the cells in B
with NA if and only if the corresponding cell in A is NA.
I have search extensively for a method to do this, and I'm sure that in
the end the solution will be embarrassingly simple, however, any help is
greatly appreciated!

Cheers,

Carson

Apologies if this has been posted twice, we are currently experiencing 
server problems...

Try 
bb[is.na(aa)] <- NA

It may be simple but it is not necessarily obvious :)
--- Carson Farmer <cfarmer at uvic.ca> wrote:
> Dear List,
> 
> I am looking for an efficient method for replacing
> values in a
> data.frame conditional on the values of a separate
> data.frame. Here is
> my scenario:
> I have a data.frame (A) with say 1000 columns, and
> 365 rows. Each cell
> in the data.frame has either valid value, or NA. I
> have an additional
> data.frame (B) with the same number of rows and
> columns, with valid
> values in all cells. What I would like to do, is
> replace the cells in B
> with NA if and only if the corresponding cell in A
> is NA.
> I have search extensively for a method to do this,
> and I'm sure that in
> the end the solution will be embarrassingly simple,
> however, any help is
> greatly appreciated!
> 
> Cheers,
> 
> Carson
> 
> Apologies if this has been posted twice, we are
> currently experiencing 
> server problems...
> 
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