[R] More efficient way to use ifelse()?

[Ian Dworkin]

# This is more about trying to find a more effecient way to code some
simple vectorized computations using ifelse().

# Say you have some vector representing a factor with a number of
levels (6 in this case), representing the location that samples were
collected.

Population <- gl( n=6, k=5,length=120, labels =c("CO", "CN","Ga","KO",
"Mw", "Ng"))


# You would like to assign a particular value to each level of
population (in this case the elevation at which they were collected).
In a vectorized approach (for speed... pretend this was a big data
set..)

elevation <-  ifelse(Population=="CO", 2169,
 ifelse(Population=="CN", 1121,
  ifelse(Population=="Ga", 500,
    ifelse(Population=="KO", 2500,
    	ifelse(Population=="Mw", 625,
    	  ifelse(Population=="Ng", 300, NA ))))))
    	
# Which is fine, but is a pain to write...

# So I was trying to think about how to vectorize directly. i.e use
vectors within the test, and for return values for T and F

elevation.take.2 <- ifelse(Population==c("CO",  "CN", "Ga", "KO",
"Mw", "Ng"), c(2169, 1121, 500, 2500, 625, 300), c(NA, NA, NA, NA, NA,
NA))

# It makes sense to me why this does not work (elevation.take.2), but
I am not sure how to get it to work. Any suggestions? I suspect it
involves a trick using "any" or "II" or something, but I can't seem to
work it out.


# Thanks in advance!

# Ian Dworkin
# idworkin at msu.edu