R help - Mar 2010 - Substitute NAs in a data frame

Excuse me for what I'm sure is a stupid beginner's question, but
I've
given up trying to find the answer to this question from the help, 
RSiteSearch, or any of the usual places.

I have a list that looks like this:
 >myList
$first
[1] "--" "18" "8" "32"

$second
[1] "--" "--" "40" "54"

I want a straightforward way to replace "--" with NA so that the list 
looks like:

 >myList
$first
[1] NA "18" "8" "32"

$second
[1] NA NA "40" "54"

Now I know I can do something like:

     myList$first <- sub("--",NA,myList$first)

but the real list has lots of components. So is there some easy way to 
do something like:

     myList <- applier(myList,sub,"--",NA)

where "applier" is a function that will do what I want? I tried using 
lapply, sapply, etc. without luck.

     Thank,
     Marsh

Marsh wrote:
> 
> Excuse me for what I'm sure is a stupid beginner's question, but
I've
> given up trying to find the answer to this question from the help, 
> RSiteSearch, or any of the usual places.
> 
> I have a list that looks like this:
>  >myList
> $first
> [1] "--" "18" "8" "32"
> 
> $second
> [1] "--" "--" "40" "54"
> 
> I want a straightforward way to replace "--" with NA so that the
list
> looks like:
> 
>  >myList
> $first
> [1] NA "18" "8" "32"
> 
> $second
> [1] NA NA "40" "54"
> 
> Now I know I can do something like:
> 
>      myList$first <- sub("--",NA,myList$first)
> 
> but the real list has lots of components. So is there some easy way to 
> do something like:
> 
>      myList <- applier(myList,sub,"--",NA)
> 
> where "applier" is a function that will do what I want? I tried
using
> lapply, sapply, etc. without luck.
> 
>      Thank,
>      Marsh
> 
You had it correct if you use lapply, you just need to name the additional
arguments you are passing:

  myList <- lapply( myList, sub, pattern = '--', replacement = NA )

The sub-lists of myList will be positionally matched to the third argument
of the sub function, which is x.

Hope this helps!

-Charlie

-----
Charlie Sharpsteen
Undergraduate-- Environmental Resources Engineering
Humboldt State University
-- 
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