Using the match Function in Dataframes
The worms dataframe (above) contains fields of five different vegetation types:
unique(worms$Vegetation)
[1] Grassland Arable Meadow Scrub Orchard
and we want to know the appropriate herbicides to use in each of the 20 fields. The herbicides are in a separate dataframe that contains the recommended herbicides for a much larger set of plant community types:
herbicides<-read.table("c:\\temp\\herbicides.txt",header=T) herbicides
Type Herbicide 1 Woodland Fusilade 2 Conifer Weedwipe 3 Arable Twinspan 4 Hill Weedwipe 5 Bracken Fusilade 6 Scrub Weedwipe 7 rassland Allclear 8 Chalk Vanquish 9 Meadow Propinol 10 Lawn Vanquish 11 Orchard Fusilade 12 Verge Allclear
The task is to create a vector of length 20 (one for every field in worms) containing the name of the appropriate herbicide. The first value needs to be Allclear because Nash's Field is grassland, and the second needs to be Twinspan because Silwood Bottom is arable, and so on. The first vector in match is worms$Vegetation and the second vector in match is herbicides$Type. The result of this match is used as a vector of subscripts to extract the relevant herbicides from herbicides$Herbicide like this:
herbicides$Herbicide[match(worms$Vegetation,herbicides$Type)]
[1] Allclear Twinspan Allclear Propinol Weedwipe Allclear
Allclear Twinspan
[9] Fusilade Allclear Weedwipe Allclear Allclear Allclear
Propinol Propinol
[17] Weedwipe Twinspan Allclear Weedwipe
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