-----Message d'origine-----
De : owner-r-help at stat.math.ethz.ch
[mailto:owner-r-help at stat.math.ethz.ch]De la part de Prof Brian D Ripley
Envoye : Thursday, January 11, 2001 1:45 PM
A : Yu-Ling Wu
Cc : R-help at stat.math.ethz.ch
Objet : Re: [R] read data into R with some constraints
On Thu, 11 Jan 2001, Yu-Ling Wu wrote:
Hi,
I have a big data file (over 30,000 records) looks
like this:
100, 20, 46, 70
103, 0, 22, 45
117, -1, 34, 65
120, 15, 0, 25
113, 0, -1, 32
142, -1, -1, 55
.....
I want to read only those records having positive
values in all of the four
columns. That is, I don't want to read record # 3, 5,
and 6 into R. However,
when I type:
read.csv("data.csv", sep=",") -> rawdata
Um, read.csv uses sep =",", and you need header=FALSE.
it reads the whole thing into R including those
records I don't want.
Could anyone tell me how I can read only those records
I want?
You can't! Until you have read the record, you cannot tell if all the
entries are positive.
Is this really a problem? You only have around 120k numbers, and I just
did it very easily.
rawdata <- read.csv("data.csv", header=F)
Perhaps better is to use a matrix and scan():
rawdata <- matrix(scan("data.csv", sep=","), , 4, byrow=TRUE)
keep <- (rawdata <= 0) %*% rep(1,4) == 0
rawdata[keep, ]
Takes a few seconds and a few Mb.
--
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 272860 (secr)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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