R Arrays

How it works

An R array adds dimensions to an atomic vector. A three-dimensional array can represent desk, period and day, but those meanings come from your data design, not from array itself. dimnames make selections easier to read. As with matrices, dropped dimensions can surprise a function that expects a stable shape.

Run this R example

These examples run locally with R, not PHP, Python or JavaScript. The reviewed baseline is R 4.5.2 on Windows x64/UCRT, using only packages shipped with R. This is a tested version, not a newest-release claim. Install your own R from the official R project; an IDE is optional. Save the complete source as arrays.R in a separate learning folder and run Rscript --vanilla arrays.R. Keep code and fictional fixtures separate from a real project.

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Example

local({
  previous_options <- options(warn = 2, digits = 8, stringsAsFactors = FALSE)
  on.exit(options(previous_options), add = TRUE)
  counts <- array(1:8, dim = c(2, 2, 2),
    dimnames = list(desk = c("A", "B"), period = c("AM", "PM"), day = c("Mon", "Tue")))
  cat("shape:", paste(dim(counts), collapse = "x"), "\n")
  cat("A PM Tue:", counts["A", "PM", "Tue"], "\n")
  cat("AM shape:", paste(dim(counts[, "AM", , drop = FALSE]), collapse = "x"), "\n")
  invisible(NULL)
})

counts <- array(1:8, dim = c(2, 2, 2),
  dimnames = list(desk = c("A", "B"), period = c("AM", "PM"), day = c("Mon", "Tue")))
cat("shape:", paste(dim(counts), collapse = "x"), "\n")
cat("A PM Tue:", counts["A", "PM", "Tue"], "\n")
cat("AM shape:", paste(dim(counts[, "AM", , drop = FALSE]), collapse = "x"), "\n")

Expected result

shape: 2x2x2
A PM Tue: 7
AM shape: 2x1x2

The example assigns a distinct meaning to each axis. The selected AM block keeps a one-element period dimension. These are synthetic values for indexing practice, not observations collected from real desks.