[R] difficult data manipulation question

[Gabor Grothendieck]

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 at verizon.net <markleeds at 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
>
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