Message-ID: <alpine.LRH.2.00.0902271642510.29839@reclus.nhh.no>
Date: 2009-02-27T15:44:51Z
From: Roger Bivand
Subject: Using a mask
In-Reply-To: <49A7FA2B.4090807@amnh.org>
On Fri, 27 Feb 2009, Ned Horning wrote:
> Is there an easy way to mask (or flag) data values in R so they do not get
> processed. I am using predict.randomForest on a satellite image and there are
> a lot (~30%) of pixels with a value of "0" that I'd prefer not to process
> with predict.randomForest to save time. I was thinking it might be possible
> to create a data frame with valid data for each line read from the input
> multi-band image and then reconstruct the line before writing it out but I
> think the overhead would be very high. At least using the brute force methods
> like rbind.
It looks as though setting the values to NA will work. In the
predict.randomForest example, do:
df <- iris[ind == 2,]
is.na(df[1:10, 1:2]) <- TRUE
predict(iris.rf, df)
So setting the 0 values to NA might get you the results you want,
maintaining the relative order of the observations.
Roger
>
> All the best,
>
> Ned
>
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--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no