Re: [R] cbind() and factors.
Gabor Grothendieck wrote:
michael watson (IAH-C michael.watson at bbsrc.ac.uk writes:
:
: Hi
:
: I'm seeing some odd behaviour with cbind(). My code is:
:
: cat - read.table(cogs_category.txt, sep=\t, header=TRUE,
: quote=NULL, colClasses=character)
: colnames(cat)
: [1] CodeDescription
: is.factor(cat$Code)
: [1] FALSE
: is.factor(cat$Description)
: [1] FALSE
: is.factor(rainbow(nrow(cat)))
: [1] FALSE
: cat - cbind(cat,Color=rainbow(nrow(cat)))
: is.factor(cat$Color)
: [1] TRUE
: ?cbind
:
: I read a text file in which has two columns, Code and Description.
: Neither of these are factors. I want to add a column of colours to the
: data frame using rainbow(). The rainbow function also does not return a
: factor. However, if I cbind my data frame (which has no factors in it)
: and the results of rainbow() (which is a vector, not a factor), then for
: some reason the new column is a factor...??
Others have already explained the problem and given what is likely
the best solution but here is one other idea, just in case.
You may require a data frame depending on what you want to do but
if you don't then you could alternately use a character matrix
since that won't result in any conversions to factor.
Lets call the data frame from read.table, Cat.df, and our
matrix, Cat.m. cat is not wrong but its confusing
since there is a common R function called cat. Now we can
write the following and don't have to worry about factors:
Cat.df - read.table(...)
# create a character matrix and cbind Colors to it
Cat.m - cbind(as.matrix(Cat.df), Color = rainbow(nrow(Cat.df)))
If you do find you need a data frame later you can convert it back
like this:
Cat.df - as.data.frame(Cat.m)
Cat.df[] - Cat.m # clobber factors with character data
For speed, the mApply function in the Hmisc package (used by the Hmisc
summarize function) does looping for stratified statistical summaries by
operating on matrices rather than data frames. factors are converted
to numerics, and service routines can save and restore the levels and
other attributes. Here is an example from the summarize help file, plus
related examples:
# To run mApply on a data frame:
m - mApply(asNumericMatrix(x), race, h)
# Here assume h is a function that returns a matrix similar to x
at - subsAttr(x) # get original attributes and storage modes
matrix2dataFrame(m, at)
# Get stratified weighted means
g - function(y) wtd.mean(y[,1],y[,2])
summarize(cbind(y, wts), llist(sex,race), g, stat.name='y')
mApply(cbind(y,wts), llist(sex,race), g)
# Compare speed of mApply vs. by for computing
d - data.frame(sex=sample(c('female','male'),10,TRUE),
country=sample(letters,10,TRUE),
y1=runif(10), y2=runif(10))
g - function(x) {
y - c(median(x[,'y1']-x[,'y2']),
med.sum =median(x[,'y1']+x[,'y2']))
names(y) - c('med.diff','med.sum')
y
}
system.time(by(d, llist(sex=d$sex,country=d$country), g))
system.time({
x - asNumericMatrix(d)
a - subsAttr(d)
m - mApply(x, llist(sex=d$sex,country=d$country), g)
})
system.time({
x - asNumericMatrix(d)
summarize(x, llist(sex=d$sex, country=d$country), g)
})
--
Frank E Harrell Jr Professor and Chair School of Medicine
Department of Biostatistics Vanderbilt University
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Re: [R] cbind() and factors.
cat is a data.frame, so cbind is use for a data.frame and ?data.frame tell us that: Character variables passed to 'data.frame' are converted to factor columns unless protected by 'I'. PS : it is not good ides to call your data.frame cat as there is a cat function. At 09:19 10/12/2004, michael watson (IAH-C) wrote: Hi I'm seeing some odd behaviour with cbind(). My code is: cat - read.table(cogs_category.txt, sep=\t, header=TRUE, quote=NULL, colClasses=character) colnames(cat) [1] CodeDescription is.factor(cat$Code) [1] FALSE is.factor(cat$Description) [1] FALSE is.factor(rainbow(nrow(cat))) [1] FALSE cat - cbind(cat,Color=rainbow(nrow(cat))) is.factor(cat$Color) [1] TRUE ?cbind I read a text file in which has two columns, Code and Description. Neither of these are factors. I want to add a column of colours to the data frame using rainbow(). The rainbow function also does not return a factor. However, if I cbind my data frame (which has no factors in it) and the results of rainbow() (which is a vector, not a factor), then for some reason the new column is a factor...?? Mick Michael Watson Head of Informatics Institute for Animal Health, Compton Laboratory, Compton, Newbury, Berkshire RG20 7NN UK Phone : +44 (0)1635 578411 ext. 2535 Mobile: +44 (0)7990 827831 E-mail: [EMAIL PROTECTED] __ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Stéphane DRAY -- Département des Sciences Biologiques Université de Montréal, C.P. 6128, succursale centre-ville Montréal, Québec H3C 3J7, Canada Tel : (514) 343-6111 poste 1233 Fax : (514) 343-2293 E-mail : [EMAIL PROTECTED] -- Web http://www.steph280.freesurf.fr/ __ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] cbind() and factors.
This is of the nature of an FAQ. Data frames coerce character vectors into factors. If you want a character vector to stay that way (and not become a factor) wrap in up in ``I()'': cat - cbind(cat,Color=I(rainbow(nrow(cat (There's no need to quote the name ``Color'' in the foregoing.) cheers, Rolf Turner [EMAIL PROTECTED] __ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] cbind() and factors.
michael watson (IAH-C michael.watson at bbsrc.ac.uk writes: : : Hi : : I'm seeing some odd behaviour with cbind(). My code is: : : cat - read.table(cogs_category.txt, sep=\t, header=TRUE, : quote=NULL, colClasses=character) : colnames(cat) : [1] CodeDescription : is.factor(cat$Code) : [1] FALSE : is.factor(cat$Description) : [1] FALSE : is.factor(rainbow(nrow(cat))) : [1] FALSE : cat - cbind(cat,Color=rainbow(nrow(cat))) : is.factor(cat$Color) : [1] TRUE : ?cbind : : I read a text file in which has two columns, Code and Description. : Neither of these are factors. I want to add a column of colours to the : data frame using rainbow(). The rainbow function also does not return a : factor. However, if I cbind my data frame (which has no factors in it) : and the results of rainbow() (which is a vector, not a factor), then for : some reason the new column is a factor...?? Others have already explained the problem and given what is likely the best solution but here is one other idea, just in case. You may require a data frame depending on what you want to do but if you don't then you could alternately use a character matrix since that won't result in any conversions to factor. Lets call the data frame from read.table, Cat.df, and our matrix, Cat.m. cat is not wrong but its confusing since there is a common R function called cat. Now we can write the following and don't have to worry about factors: Cat.df - read.table(...) # create a character matrix and cbind Colors to it Cat.m - cbind(as.matrix(Cat.df), Color = rainbow(nrow(Cat.df))) If you do find you need a data frame later you can convert it back like this: Cat.df - as.data.frame(Cat.m) Cat.df[] - Cat.m # clobber factors with character data __ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] cbind() and factors.
Probably you called the build-in rainwbow-function, which returns a string. str(rainbow(10)) chr FF Dieter Menne __ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
