[Rd] matrix operations
Prof Brian Ripley
ripley at stats.ox.ac.uk
Sun Feb 20 20:13:36 CET 2005
On Sun, 20 Feb 2005, Melanie Vida wrote:
> In R, I'm imported a data frame of 2,321,123 by 4 called "dataF".
> I converted the data frame "dataF" to a matrix
> dataM <- as.matrix(dataF)
I am assuming this is a numeric matrix, and "inf" means Inf and in places
that there are no NAs.
> Does R have an efficient routine to treat the special elements that contain
> "inf" in them. For example, can you separate the rows that have "inf"
> elements from the matrix into a separate matrix without iterating over the
> entire matrix?
Not really, but is.infinite will do a C-level iteration, as will ==
dataM[rowSums(is.infinite(dataM)) > 0, ] # rows containing Inf or -Inf
dataM[rowSums(dataM == Inf), ] # rows containing Inf (no NAs)
A <- !is.na(dataM) & dataM == Inf
dataM[rowSums(A), ] # rows containing Inf (possible NAs)
> Also, does R have an efficient way to sort columns in a matrix?
for(i in 1:4) dataM[, i] <- sort(dataM[, i], method ="quick")
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
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