I'm not sure if this is a bug, or if I'm doing something wrong.
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=46rom the worms dataframe, which is at in a file called worms.txt at
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http://www.imperial.ac.uk/bio/research/crawley/therbook
<http://www.imperial.ac.uk/bio/research/mjcraw/therbook/index.htm>=20
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the idea is to extract a subset of the rows, sorted in declining order
of worm density, with only the maximum worm density from each vegetation
type:
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worms<-read.table("c:\\temp\\worms.txt",header=3DT)
attach(worms)
names(worms)
[1] "Field.Name" "Area" "Slope" "Vegetation"
"Soil.pH"=20=20=20=20=20
[6] "Damp" "Worm.density"
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Usinng "not duplicated" I get two rows for Meadow and none for Scrub
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worms[rev(order(Worm.density)),] [!duplicated(Vegetation),]
Field.Name Area Slope Vegetation Soil.pH Damp Worm.density
9 The.Orchard 1.9 0 Orchard 5.7 FALSE 9
16 Water.Meadow 3.9 0 Meadow 4.9 TRUE 8
10 Rookery.Slope 1.5 4 Grassland 5.0 TRUE 7
2 Silwood.Bottom 5.1 2 Arable 5.2 FALSE 7
4 Rush.Meadow 2.4 5 Meadow 4.9 TRUE 5
and here is the correct set of rows, but in the wrong order, using
unique
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worms[rev(order(Worm.density)),] [unique(Vegetation),]
Field.Name Area Slope Vegetation Soil.pH Damp Worm.density
16 Water.Meadow 3.9 0 Meadow 4.9 TRUE 8
9 The.Orchard 1.9 0 Orchard 5.7 FALSE 9
11 Garden.Wood 2.9 10 Scrub 5.2 FALSE 8
2 Silwood.Bottom 5.1 2 Arable 5.2 FALSE 7
10 Rookery.Slope 1.5 4 Grassland 5.0 TRUE 7
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Best wishes,
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Mick
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Prof M.J. Crawley FRS
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Imperial College London
Silwood Park
Ascot
Berks
SL5 7PY
UK
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Phone (0) 207 5942 216
Fax (0) 207 5942 339
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