R help - Feb 2011 - Help me apply mapply

Hello all I would like to ask your help use mapply.

I have a function called findCell that takes two arguments(x,sr)
where x is a vector of size two (e.g x<-c(2,3) and sr is a matrix.

I would like to call many times the findCell function (thus I need mapply) for
different x inputs but always for the same sr.

as x is a vector of size two (two cells) I want to pass inside inside the
following 2*10 matrix.
-The first input is the two elements of the first row  cbin(test[1,1],test[1,2])
-the second input is cbind(test[2,1],test[2,2]
-the third input is cbind(test[3,1],test[3,2]

and so on

This is the str:
str(cbind(test[,1],test[,2]))
 num [1:30, 1:2] -1 -0.667 -0.333 0 0.333 ...

so I tried the following:
> mapply(findCell,x=cbind(test[,1],test[,2]),sr=sr)
Error in if (!is.finite(length.out) || length.out < 0L) stop("length
must be non-negative number") else if (length.out ==  :
  missing value where TRUE/FALSE needed
Calls: mapply -> .Call -> <Anonymous> -> seq -> seq.default

I have spend time reading the ?mapply but I am not sure what is the problem
here. Could you please help me understand what is missing?

Best Regards
Alex

Goodmorning List Member,
I would like to ask your help using mapply or Vectorize to make a loop more
efficient.
I have a m*4 matrix called borders and I would like to add a 5th column. Thus
first
A. I add the new 5th column
borders<-cbind(borders,matrix(data=NA,nrow=nrow(borders)))
B. For every cell in this new column I call a function and I put the results in
for (i in c(1:nrow(borders))) # How can I can improve that with mapply?
	borders[i,5]<-findCell(c(borders[i,1],borders[i,2]),sr)

As you can see from B I call a function called findCell that takes as input two
arguments
-x: a vector with two cells thus the c(borders[i,1],borders[i,2]) 
-sr: a matrix that is always the same (this input is always constant)

Then I tried to change the loop in B and use mapply.
mapply(findCell,x=cbind(test[,1],test[,2]),sr=sr)
> Error in if (!is.finite(length.out) || length.out < 0L)
> stop("length must be non-negative number") else if
> (length.out ==? : 
> ? missing value where TRUE/FALSE needed
> Calls: mapply -> .Call -> <Anonymous> -> seq
> -> seq.default
I would be grateful if you can help me understand me what this error message is
about.

Best Regards
Alex

Hi

Well, no data so a wild guess. You want select values from matrix sr based 
on values in borders[,1] and borders[,2].

If it is the case plain selection could be far better
> mat<-matrix(1:12, 4,4)
> mat
     [,1] [,2] [,3] [,4]
[1,]    1    5    9    1
[2,]    2    6   10    2
[3,]    3    7   11    3
[4,]    4    8   12    4
> b1<-sample(1:4, 3)
> b2<-sample(1:4, 3)
> cbind(b1,b2)
     b1 b2
[1,]  3  2
[2,]  4  1
[3,]  2  3
> mat[cbind(b1,b2)]
[1]  7  4 10
>
If you want something else please provide some sample code and data which 
can be used for reproduction of your problem.
>From the error it seems that your function is somehow incompatible with 
mapply expectation.

Regards
Petr


r-help-bounces at r-project.org napsal dne 03.02.2011 10:59:34:
> Goodmorning List Member,
> I would like to ask your help using mapply or Vectorize to make a loop 
more efficient.
> I have a m*4 matrix called borders and I would like to add a 5th column. 
Thus first
> A. I add the new 5th column
> borders<-cbind(borders,matrix(data=NA,nrow=nrow(borders)))
> B. For every cell in this new column I call a function and I put the 
results in
> for (i in c(1:nrow(borders))) # How can I can improve that with mapply?
>    borders[i,5]<-findCell(c(borders[i,1],borders[i,2]),sr)
> 
> As you can see from B I call a function called findCell that takes as 
input 
> two arguments 
> -x: a vector with two cells thus the c(borders[i,1],borders[i,2]) 
> -sr: a matrix that is always the same (this input is always constant)
> 
> Then I tried to change the loop in B and use mapply.
> mapply(findCell,x=cbind(test[,1],test[,2]),sr=sr)
> > Error in if (!is.finite(length.out) || length.out < 0L)
> > stop("length must be non-negative number") else if
> > (length.out ==  : 
> >   missing value where TRUE/FALSE needed
> > Calls: mapply -> .Call -> <Anonymous> -> seq
> > -> seq.default
> 
> I would be grateful if you can help me understand me what this error 
message is about.
> 
> Best Regards
> Alex
> 
> 
> 
> 
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