[R] Beginner's query - segmentation fault

[Prof Brian Ripley]

On Tue, 7 Oct 2003, Laura Quinn wrote:

> I am dealing with a huge matrix in R (20 columns, 54000 rows) and have
> lots of missing values within the dataset which are currently displayed as
> the value "-999.00" I am trying to create a new matrix (or change the
> existing one) to display these values as "NA" so that I can then perform
> the necessary analysis on the columns within the matrix.
> 
> The matrix name is temp and the column names are t1 to t20 inclusive.
> 
> I have tried the following command:
> 
> temp$t1[temp$t1 == -999.00] <- NA
> 
> and it returns a segmentation fault, can someone tell me what I am doing
> wrong?

Well, R should not segfault, so there is bug here somewhere.  However, I
don't think what you have described can actually work. Is temp really a
matrix?  If so temp$t1 will return NULL, and you should get an error
message.


If temp is a matrix

temp[temp == -999.00] <- NA

will do what you want.


If as is more likely temp is a data frame with all columns numeric,
there are several ways to do this, e.g.

temp[] <- lapply(temp, function(x) ifelse(x == -999, NA, x))

temp[as.matrix(temp) == -999] <- NA  # only in recent versions of R

as well as explicit looping over columns.

-- 
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