Sacha -
The "$" notation can only be used when you literally use
the name of the column you want. If the name of the column
is stored in a variable, you should use this notation:
maptable[,value]
to refer to the column whose name is stored in "value".
- Phil Spector
Statistical Computing Facility
Department of Statistics
UC Berkeley
spec...@stat.berkeley.edu
On Tue, 16 Mar 2010, Sacha Viquerat wrote:
hello! ive come across the following problem:
im writing a function to ease the production of maps. as my tables have
headers, id like to include an option in my function header to pass these
columns to use them inside the evaluation block. the function looks as
follows:
# maptable #the name of the table containing coordinates and columns for
measured values
# value: which column of my table to use (e.g. Alt, slope, us, etc...
# labels(maptable)
# [1] "pos.e" "pos.n" "Alt" "slope" "us" "uus" "lc"
make.map<-function (maptable,value)
{
pos.e<-maptable$pos.e #calling the column directly works
pos.n<-maptable$pos.n #calling the column directly works
key<-maptable$value #this doesnt work. output: NULL
... rest of function, irrelevant to my question
}
for example, i call the function by:
make.map(elevation,Alt,"Altitude","Sightings")
and my interp from akima package denies work, since key is NULL
interp(pos.e,pos.n,key,...)
have i just missed something? ive browsed the help pages and the archive,
looked into crawleys R book but didnt find any solution, though im pretty
sure this should be achievable!
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and provide commented, minimal, self-contained, reproducible code.
