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: [email protected]
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