[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
> 
> 
> 
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> and provide commented, minimal, self-contained, reproducible code.
Hello,

Something like this?



names_cols <- function(x, First = "NSims", Prefix = "Value") {
   nms <- c(First, sprintf("%s%d", Prefix, seq_len(ncol(x) - 1L)))
   colnames(x) <- nms
   x
}

NSims <- 4
Grps <- 5
DiffMeans <- matrix(nrow=NSims,ncol=1+Grps)
names_cols(DiffMeans)
#>      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


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