[R] Create matrix with variable number of columns AND CREATE NAMES FOR THE COLUMNS

[Rui Barradas]

Às 16:54 de 01/07/2024, Sorkin, John escreveu:
> #I am trying to write code that will create a matrix with a variable number of columns where the #number of columns is 1+Grps
> #I can do this:
> NSims <- 4
> Grps <- 5
> DiffMeans <- matrix(nrow=NSims,ncol=1+Grps)
> DiffMeans
> 
> #I have a problem when I try to name the columns of the matrix. I want the first column to be NSims, #and the other columns to be something like Value1, Value2, . . . Valuen where N=Grps
> 
> # I wrote a function to build a list of length Grps
> createValuelist <- function(num_elements) {
>    for (i in 1:num_elements) {
>      cat("Item", i, "\n", sep = "")
>    }
> }
> createValuelist(Grps)
> 
> # When I try to assign column names I receive an error:
> #Error in dimnames(DiffMeans) <- list(NULL, c("NSim", createValuelist(Grps))) :
> # length of 'dimnames' [2] not equal to array extent
> dimnames(DiffMeans) <- list(NULL,c("NSim",createValuelist(Grps)))
> DiffMeans
> 
> # Thank you for your help!
> 
> 
> John David Sorkin M.D., Ph.D.
> Professor of Medicine, University of Maryland School of Medicine;
> Associate Director for Biostatistics and Informatics, Baltimore VA Medical Center Geriatrics Research, Education, and Clinical Center;
> PI Biostatistics and Informatics Core, University of Maryland School of Medicine Claude D. Pepper Older Americans Independence Center;
> Senior Statistician University of Maryland Center for Vascular Research;
> 
> Division of Gerontology and Paliative Care,
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> Cell phone 443-418-5382
> 
> 
> 
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
Hello,

Sorry for my first answer, I thought you only wanted to name the matrix 
columns. After reading the OP again, this time actually reading it, I 
realized you also want to create the matrix. This is even in the 
question title line :(.



create_matrix <- function(nsims, ngrps, First = "NSims", Prefix = "Value") {
   # could also be paste0(Prefix, seq_len(ngrps))
   grp_names <- sprintf("%s%d", Prefix, seq_len(ngrps))
   nms <- c(First, grp_names)
   matrix(nrow = nsims, ncol = 1L + ngrps, dimnames = list(NULL, nms))
}

NSims <- 4
Grps <- 5
create_matrix(NSims, Grps)
#>      NSims Value1 Value2 Value3 Value4 Value5
#> [1,]    NA     NA     NA     NA     NA     NA
#> [2,]    NA     NA     NA     NA     NA     NA
#> [3,]    NA     NA     NA     NA     NA     NA
#> [4,]    NA     NA     NA     NA     NA     NA



Hope this helps,

Rui Barradas


-- 
Este e-mail foi analisado pelo software antivírus AVG para verificar a presença de vírus.
www.avg.com