R help - Jan 2011 - Match numeric vector against rows in a matrix?

Two posts in one day is not a good day...and this question seems like it should
have an obvious answer:

I have a matrix where rows are unique combinations of 1's and 0's:
> combs=as.matrix(expand.grid(c(0,1),c(0,1)))
> combs
     Var1 Var2
[1,]    0    0
[2,]    1    0
[3,]    0    1
[4,]    1    1

I want a single function that will give the row index containing an exact match
with vector x:
> x=c(0,1)
The solution needs to be applied many times, so I need something quick -- I was
hoping a base function would do it, but I'm drawing a blank.

Thanks!
Kevin

On Jan 5, 2011, at 2:16 PM, Kevin Ummel wrote:
> Two posts in one day is not a good day...and this question seems  
> like it should have an obvious answer:
>
> I have a matrix where rows are unique combinations of 1's and 0's:
>
>> combs=as.matrix(expand.grid(c(0,1),c(0,1)))
>> combs
>     Var1 Var2
> [1,]    0    0
> [2,]    1    0
> [3,]    0    1
> [4,]    1    1
>
> I want a single function that will give the row index containing an  
> exact match with vector x:
>
>> x=c(0,1)
 > intersect( which(combs[,1]==x[1]), which(combs[,2]==x[2]) )
[1] 3

Or maybe even faster:

 >  which( combs[,1]==x[1] & combs[,2]==x[2])
[1] 3
>
> The solution needs to be applied many times, so I need something  
> quick -- I was hoping a base function would do it, but I'm drawing a  
> blank.
>
-- 

David Winsemius, MD
West Hartford, CT

On Wed, Jan 05, 2011 at 07:16:47PM +0000, Kevin Ummel
wrote:
> Two posts in one day is not a good day...and this question seems like it
should have an obvious answer:
> 
> I have a matrix where rows are unique combinations of 1's and 0's:
> 
> > combs=as.matrix(expand.grid(c(0,1),c(0,1)))
> > combs
>      Var1 Var2
> [1,]    0    0
> [2,]    1    0
> [3,]    0    1
> [4,]    1    1
> 
> I want a single function that will give the row index containing an exact
match with vector x:
> 
> > x=c(0,1)
> 
> The solution needs to be applied many times, so I need something quick -- I
was hoping a base function would do it, but I'm drawing a blank.
If the matrix can have different number of columns, then
also the following can be used

  combs <- as.matrix(expand.grid(c(0,1),c(0,1),c(0,1)))
  x <- c(0,1,1)
  which(rowSums(combs != rep(x, each=nrow(combs))) == 0) # [1] 7

Petr Savicky.

Try this:

 which(colSums(t(combs) == x) == ncol(combs))

On Wed, Jan 5, 2011 at 5:16 PM, Kevin Ummel <kevinummel@gmail.com> wrote:
> Two posts in one day is not a good day...and this question seems like it
> should have an obvious answer:
>
> I have a matrix where rows are unique combinations of 1's and 0's:
>
> > combs=as.matrix(expand.grid(c(0,1),c(0,1)))
> > combs
>     Var1 Var2
> [1,]    0    0
> [2,]    1    0
> [3,]    0    1
> [4,]    1    1
>
> I want a single function that will give the row index containing an exact
> match with vector x:
>
> > x=c(0,1)
>
> The solution needs to be applied many times, so I need something quick -- I
> was hoping a base function would do it, but I'm drawing a blank.
>
> Thanks!
> Kevin
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

	[[alternative HTML version deleted]]

Hi Petr,

Sorry for the delay. I ended up implementing a simple and fast but not-universal
or elegant solution, since it turned out that I only needed to test a rather
small subset of combinations for my purposes.

Nevertheless, I did go back and try the solutions posted. Bill's 'binary
expansion' approach was the fastest by about a factor of 8.

Cheers,
Kevin

On Jan 11, 2011, at 9:20 AM, Petr Savicky wrote:
> Dear Kevin Ummel:
> 
> There were several suggestions on R-help concering your question below.
> None of them suggests a base function. I would also expect that
> there is a base function for matching the rows. A related function is
> dist(), but it takes only one matrix as input and computes the distances
> between all pairs of its rows. Matching only some rows would require
> a modification of dist(), which would take two matrices and compare
> rows of one of them to the rows of the other. However, i do not know
> such a function in R.
> 
> Is some of the suggestions on R-help suitable for your purposes?
> 
> Thank you in advance for your kind reply.
> 
> Best regards, Petr Savicky.
> 
> On Wed, Jan 05, 2011 at 07:16:47PM +0000, Kevin Ummel wrote:
>> Two posts in one day is not a good day...and this question seems like
it should have an obvious answer:
>> 
>> I have a matrix where rows are unique combinations of 1's and
0's:
>> 
>>> combs=as.matrix(expand.grid(c(0,1),c(0,1)))
>>> combs
>>     Var1 Var2
>> [1,]    0    0
>> [2,]    1    0
>> [3,]    0    1
>> [4,]    1    1
>> 
>> I want a single function that will give the row index containing an
exact match with vector x:
>> 
>>> x=c(0,1)
>> 
>> The solution needs to be applied many times, so I need something quick
-- I was hoping a base function would do it, but I'm drawing a blank.
>> 
>> Thanks!
>> Kevin
>> 
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>