# 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
Hi:
Look into switch(), something like
elevation <- switch(Population,
'CO' = 2169,
'CN' = 1121,
...
)
HTH,
Dennis
On Tue, May 25, 2010 at 10:25 PM, Ian Dworkin <idworkin@msu.edu> wrote:
> # 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@msu.edu
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
[[alternative HTML version deleted]]
Ian Dworkin wrote:> # 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. >In a case like this, often indexing is clearer than ifelse. For example, results <- c(CN=1121, Ga = 500, KO=2500, Mw = 625, Ng = 300) elevation <- results[Population] Generally vector indexing of atomic vectors and matrices is very fast; indexing of data frames is much slower, so if speed is an issue, avoid them. Duncan Murdoch
Hi Ian. Take a look at the recode function in the car package. HTH, Jorge On Wed, May 26, 2010 at 1:25 AM, Ian Dworkin <> wrote:> # 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@msu.edu > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >[[alternative HTML version deleted]]
On May 26, 2010, at 1:25 AM, Ian Dworkin wrote:> # 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 ))))))elevation <- (Population=="CO")* 2169+ (Population=="CN")* 1121+ (Population=="Ga")* 500+ (Population=="KO")* 2500+ (Population=="Mw")* 625+ (Population=="Ng")* 300 is.na(elevation) <- elevation==0> # Which is fine, but is a pain to write...Also approaching the nesting limits (seven levels if I remember) of the ifelse function.> > # 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 > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code.David Winsemius, MD West Hartford, CT