[R] 3 questions regarding matrix copy/shuffle/compares

[David Winsemius]

On Apr 26, 2009, at 12:28 AM, Esmail wrote:

> Hello all,
>
> I have the following function call to create a matrix of POP_SIZE rows
> and fill it with bit strings of size LEN:
>
>   pop=create_pop_2(POP_SIZE, LEN)

Are you construction a vector or a matrix? What are the dimensions of  
your matrix?

>
>
> I have 3 questions:
>
> (1) If I did
>
>    keep_pop[1:POP_SIZE] == pop[1:POP_SIZE]
>
>    to keep a copy of the original data structure before manipulating
>    'pop' potentially, would this make a deep copy or just shallow? Ie
>    if I change something in 'pop' would it be reflected in 'keep_pop'
>    too? (I don't think so, but just wanted to check). I would like
>    two independent copies.

"==" is not an assignment operator in R, so the answer is that it  
would do neither.
"<-" and "=" can do assignment. In neither case would it be a "deep  
copy".
>
>
> (2) If I wanted to change the order of *rows* in my matrix 'pop', is  
> there
>    an easy way to shuffle these? I don't want to change anything in  
> the
>    columns, just the complete rowsn (E.g., in Python I could just say
>    something like suffle(pop) assuming pop is a list of list) - is  
> there
>    an equivalent for R?

You can get a value from a matrix by using the indexing construction.  
But your
terminology is confusing. Is pop a matrix or a list?

?"["
?order
... and perhaps ?sample if you wanted a random permutation of the rows.

I am going to refrain from posting speculation until you provide valid  
R code
that will create an object that can be the subject of operations.



> (3) I would like to compare the contents of 'keep_pop' with 'pop'.  
> Though
>    the order of rows may be different it should not matter as long as
>    the same rows are present. Again, in Python this would be simply
>
>    if sorted(keep_pop) == sorted(pop):
>       print 'they are equal'
>    else
>       print 'they are not equal'
>
>    Is there an equivalent R code segment?

Depends on what you want to do and what you are doing it on. You could  
look at:

?%in%
?merge

>
>
> Thanks,
>
> Esmail
>
> --------------- the code called above -------------

The code below creates a "bit vector" but then only makes exact  
multiples of it
in the first row and zeros in the second row. Was that what was desired?


> ####################################################
> # create a binary vector of size "len"
> #
> create_bin_Chromosome <- function(len)
> {
>  sample(0:1, len, replace=T)
> }
>
>
>
> ############## create_population ###################
> # create population of chromosomes of length len
> # the matrix contains twice as much space as popsize
> #
> create_pop_2 <- function(popsize, len)
> {
>  datasize=len*popsize
>  print(datasize)
>  npop <- matrix(0, popsize*2, len, byrow=T)
>
>  for(i in 1:popsize)
>    npop[i,] = create_bin_Chromosome(len)
>
>  npop
> }
>


David Winsemius, MD
Heritage Laboratories
West Hartford, CT