[R] difficult data manipulation question
Gabor Grothendieck
ggrothendieck at gmail.com
Mon Jul 3 22:58:14 CEST 2006
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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