Message-ID: <Pine.LNX.4.61.0505170834280.5878@gannet.stats>
Date: 2005-05-17T07:46:19Z
From: Brian Ripley
Subject: NA erase your data trick
In-Reply-To: <4289901C.60608@statistik.uni-dortmund.de>
On Tue, 17 May 2005, Uwe Ligges wrote:
> 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?
>
> As you got it the first time. There is nothing like "undo".
>
>
>> B) How do I do it right next time, I learned my lesson, I'll never do it
>> again, I promise!
>
> By vectorization:
>
> tcn5[tcn5 == -9] <- NA
That will work if tcn5 contains NAs, but only because NA indices on the
lhs are now ignored for matrices (if tcn5 is a matrix, which seems
unstated) -- this used not to be the case. I would prefer
tcn5[tcn %in% -9] <- NA
Using %in% rather than == in computed indices is a good habit to acquire:
it also makes things like
tcn5[tcn %in% c(-9, -99)] <- NA
work as expected.
If tcn is a data frame, you have to do this column-by-column, as in
tcn5[] <- lapply(tcn5, function(x) x[x %in% -9] <- NA)
or by a logical index matrix, which is harder to construct.
>>> 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
>> +
>> + }
>> + }
--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595