[R] NA erase your data trick

Duncan Murdoch murdoch at stats.uwo.ca
Tue May 17 08:35:12 CEST 2005

Anders Schwartz Corr wrote:
> Oops,
> I just erased all my data using this gizmo that I thought would replace -9
> with NA.
> A) Can I get my tcn5 back?

Not if you don't have it backed up somewhere else.

I wouldn't recommend keeping your only copy of anything in an R 
workspace.  It's too easy to accidentally delete or overwrite it.  Keep 
the original in a file.

> B) How do I do it right next time, I learned my lesson, I'll never do it
> again, I promise!
> Anders Corr
>>for(i in 1:dim(tcn5)[2]){         ##for the number of columns
> +     for(n in 1:dim(tcn5)[1]){     ##for the number of rows
> +         tcn5[is.na(tcn5[n,i]) | tcn5[n,i] == -9] <- NA

For some values of i and n, this last line simplifies to

tcn5[TRUE] <- NA

which is why you lost your data.

You want to (a) think in vectors, or (b) use an if statement:

(a) Replace your whole series of statements with

tcn5[is.na(tcn5) | tcn5 == -9] <- NA


(b) Replace just the last line above with

   if (is.na(tcn5[n,i]) | tcn5[n,i] == -9) tcn5[n,i] <- NA

I'd choose (a); it's a lot cleaner and will run faster.

Duncan Murdoch

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