[R] logical masking of a matrix converts it to a vector
Phil Spector
spector at stat.berkeley.edu
Fri Dec 4 22:04:05 CET 2009
b <- a[rmask,,drop=FALSE]
- Phil Spector
Statistical Computing Facility
Department of Statistics
UC Berkeley
spector at stat.berkeley.edu
On Fri, 4 Dec 2009, Austin Huang wrote:
> One problem I've been having is the special case in which only one
> row/column remains and the variable gets converted into a vector when
> entries are removed by logical masking. This is a problem because subsequent
> code may rely on matrix operations (apply, colsums, dim, etc) For example:
>
>> a <- matrix(c(1, 2, 3, 4), nrow = 2)
>> a
> [,1] [,2]
> [1,] 1 3
> [2,] 2 4
>> rmask <- c(TRUE, FALSE)
>> b <- a[rmask, ]
>> colSums(b)
> Error in colSums(b) : 'x' must be an array of at least two dimensions
>
> To ensure the code works regardless of how the matrix gets modified, I need
> to explicitly recast results to a matrix, for example:
>
> b <- matrix(a[rmask, ], ncol = 2)
>
> This can get messy, requiring extra work to maintain column/row names or
> additional commands to determine the correct dimensions of the matrix (for
> example, if I'm masking both rows and columns simultaneously). Is there a
> more elegant way to deal with this in R?
>
> ~A
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> 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.
>
More information about the R-help
mailing list