bighead.R

#' bighead - show subset in each dimension
#' @description like head but in all dimensions
#' @param obj - indexable object: vector, data.frame, matrix, or array
#' @param ntotal - total maximum elements to show
bighead <- function(obj, ntotal=100){
  # dimension of object (dataframe = 2D)
  dims <- dim(obj)
  # vectors has NULL dim. Special case: set dim to length
  if(is.null(dims)) dims <- c(length(obj))
  ndim <- length(dims)

  # use ndim root of ntotal to limit each dimension
  # TODO: will be 0 if obj has a lot of dimensions ... that's no good
  n_per_dim <- floor(ntotal^(1/ndim))

  # along each dim: first to ndim-th root item (or total length of dim if smaller)
  idx <- lapply(dims, \(i) c(1:(min(i, n_per_dim))))
  # TODO: could be smarter
  #  currently always returns less than or equal to total items requested
  #  if one dim is less than what's asked, could show more in other dims

  do.call(\(...) obj[...], idx)
}

bighead_test <- function(){
   testthat::expect_equal(bighead(1:100,27),1:27)
   testthat::expect_equal(bighead(array(1:27,c(3,3,3)),9),
                          array(c(1:2,4:5,10:11,13:14),c(2,2,2)))
}