On Apr 28, 2012, at 9:18 AM, mlell08 wrote:
On Apr 28, 2012, at 8:11 AM, petermec <peter...@buffalo.edu> wrote:
Hi everyone,
I am somewhat new to R and I am trying to write a permutation
function such
that it inputs a character vector and from an arbitrary length "n"
which is
the length of the combinations for the character vector. I know
there are R
packages for permutation but this is for an assignment.
So far this is what I have:
alphabet = c("a","b","c","d")
spot = c()
permute = function(alphabet,n){
for (i in 1:factorial(length(alphabet))){
perm = sample(alphabet, replace=F, size=n)
spot = rbind(spot, perm, deparse.level=2)
}
print(spot)
}
This function works but it has some flaws for what I need. I would
like the
print output to have the rownames as the combination of the
characters for
each row (ie aa for "a" "a"). Also, this code is producing duplicate
combinations whereas I only want an output of unique combinations.
To address the rownames problem I have, I have been trying to
meddle around
with creating a dataframe from rbind with something like:
data2 = data.frame(spot, check.names=TRUE)
I was thinking something along the lines of this to remove
duplicates:
or something like make.unique(spot)
or make.names(spot, unique=TRUE)
Neither of these have been working for me. Could someone help
point me in
the right direction?
Rownames can be assigned by using rownames(dataframe) <- c("Row1",
"Row2", etc.)
The Wikipedia article about 'Permutation' holds some commonly used
Algoritms, perhaps you can find some inspiration there?
You should be able to use the 'duplicated' function to remove
duplicates by prepending its value with "!". Unlike 'make.unique',
'duplicated' is designed for working with objects having dimensions.
--
David Winsemius, MD
West Hartford, CT
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