[R] R Error : DATA to MATRIX

[Petr PIKAL]

Hi

See in text.
> 
> Dear Sir/Madam,
> 
> I'm getting a problem with a R-code which converts a data frame to a 
matrix.
> 
> It first generate a (m^(n-m) * m) matrix A and then regenerate another
> matrix B having less dimension than A which satisfy some condition. Now 
I
> wish to assign each row of B to a vector as individual.
> 
> My problem is when I set any choice of (n,m) except m=1 it works fine 
but
> setting m=1 I got the error : Error in B[i, ] : incorrect number of
> dimensions.
> 
> Moreover if (n,m) is large (say, (20,8)) I got the error : Error: cannot
> allocate vector of size 3.0 Gb. I know this is due to large dimension of
> matrix A. How to solve this problem.
> 
> My code is given below:
> 
> **********************************************************************
> 
> n=5
> m=3
> R=numeric(0)
> # Generate all possible m-tuple ( variables having range 0 to n  ) in a 
(
> m^(n-m) * m ) matrix
> 
> r = expand.grid(rep(list(0:(n-m)), m))
> 
> write.table(r,file="test.txt",row.names=FALSE,col.names=FALSE)
> 
> a= read.table(file="test.txt",sep="",header=FALSE)

Above lines do not do any sensible things. r shall be same as a.

> 
> A= data.matrix(a)
> 
> 
#.........................................................................................
> 
> # Generate matrix whose rowsum = n-m
> 
> meet.crit = apply(A, 1, function(.row) any((sum(.row)) == n-m))      # 
> criteron for being rowsum = n

No error

> 
> cbind(A, meet.crit)                                                  # 
> Checking rowsum = n for each row
> -m
> B=A[meet.crit,]                                                      # 

No error

> Generate matrix
> 
> 
#.........................................................................................
> 
> 
> for(i in 1:choose(n-1,m-1)){
> R=B[i,]
> }

No error. However in each cycle only ith row is added to R and therefore 
only last row (in this case B[6,]) is added and stays in R. Either you 
need to use

R <- c(R, B[i,])

in your construction or better as B is matrix

> class(B)
[1] "matrix"

you can transform it to vector easily by stripping dimensions.

 R<-t(B)
> dim(R) <-NULL
> R
 [1] 2 0 0 1 1 0 0 2 0 1 0 1 0 1 1 0 0 2

Regards
Petr


> 
> 
***************************************************************************
> 
> Can you please help me how to get rid of these errors. Thanking you in
> advance.
> 
> Regards
> 
> Ritwik Bhattacharya
> 
> 
> Senior Research Fellow
> SQC & OR UNIT, KOLKATA
> INDIAN STATISTICAL INSTITUTE
> 
> Voice : +91 9051253944
> 
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