Here is a modification of Gabor's solution that will return the dataframe
with just the maximum columns:


# test data
# read in header separately so R does not make column names unique
Lines <- "AAA BBB CCC DDD AAA BBB

  0      2      1     2      0      0
  2      3      7     6      0      1
  1.5    4      9     9      6      0
  1.0    6      10    11     3      3
"

DF <- read.table(textConnection(Lines), skip = 1)
names(DF) <- scan(textConnection(Lines), what = "", nlines = 1)

f <- function(x) x[which.max(colSums(DF[x]!=0))]
tapply(seq(DF), names(DF), f)


#================added code================#
# compute the number of non-zeros in each column
MostZeros <- colSums(DF != 0)
# determine which column is the maximum
x.max <- lapply(unique(names(DF)), function(.name){
 .col <- which(names(DF) == .name)  # find columns of matching names
 .max <- which.max(MostZeros[.col]) # determine max
 .col[.max]  # return the column number of the max
})
DF[unlist(x.max)]  # select only the unique maximums



On 7/3/06, Gabor Grothendieck <ggrothendieck@gmail.com> wrote:
>
> Try this:
>
> # test data
> # read in header separately so R does not make column names unique
> Lines <- "AAA BBB CCC DDD AAA BBB
>   0      2      1     2      0      0
>   2      3      7     6      0      1
>   1.5    4      9     9      6      0
>   1.0    6      10    11     3      3
> "
> DF <- read.table(textConnection(Lines), skip = 1)
> names(DF) <- scan(textConnection(Lines), what = "", nlines = 1)
>
> f <- function(x) x[which.max(colSums(DF[x]!=0))]
> tapply(seq(DF), names(DF), f)
>
> On 7/3/06, markleeds@verizon.net <markleeds@verizon.net> wrote:
> >
> > hi everyone :
> >
> > suppose i have a matrix in which some column names are identical so,
> > for example, TEMP
> >
> >  "AAA", "BBB", "CCC", "DDD","AAA", "BBB"
> >    0      2      1     2      0      0
> >    2      3      7     6      0      1
> >    1.5    4      9     9      6      0
> >    1.0    6      10    11     3      3
> >
> >
> > I didn't even check  yet whether identical column names are allowed
> > in a matrix but i hope they are.
> >
> > assuming that they are, then i would like to be able to take the matrix
> and  make a new matrix with the following requirements.
> >
> > 1) whenever there is a unique column name, just take that column for the
> new matrix
> >
> > 2) whenever the column name is not unique, take the one
> > that has the most non zero elements ? ( in the case of
> > ties, i don't care which one is picked ).
> >
> > so, in this case, the resulting matrix would just be the first 4
> columns.
> >
> > i realize ( or atleast i think ) that
> > sum( TEMP[(TEMP[,columnname] !=0) ,columnname) will give me the
> > number of non elements in a column with the name columnmame
> > but how to use this deal with the non uniqueness to solve my particular
> problem is beyond me. plus, i think the command will
> > bomb because columnname will not always be unique ?
> > Thanks for any help. I realize this is not a trivial problem so I really
> appreciate it.
> >
> >                                          Mark
> >
> > ______________________________________________
> > R-help@stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide!
> http://www.R-project.org/posting-guide.html
> >
>
> ______________________________________________
> R-help@stat.math.ethz.ch mailing list
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> PLEASE do read the posting guide!
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>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390 (Cell)
+1 513 247 0281 (Home)

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