Print a Table in markdown grid format.

mdgridtable.R

#' Print a table with text borders.
#' @param df a data.frame or matrix
#'
#' Prints a table with borders of |, -, +, and = which is usefull for 
#' formating tables to use with markdown.
#'
#' @importFrom stringr str_c str_length str_dup
#' @importFrom dostats compose
#' @export
#' @examples
#' df <- data.frame(idx=1:26, l=letters, L=LETTERS)
#' mdgridtable(df)
#' mdgridtable(matrix(1:9,3,3))
mdgridtable <- 
function(df, ...){
  m <- as.matrix(format(df, ...))
  cn <- colnames(m)
  w  <- pmax(aaply(m, 2, compose(max, str_length)),
             str_length(cn))
  
             
  (fmt <- paste("|", paste(" %", w, "s ", sep='', collapse="|"), "|", sep=''))
  pf <- function(x){do.call(sprintf, append(as.list(x), list(fmt=fmt)))}
   line <- str_c("+-", str_c(laply(w, str_dup, string='-'), collapse="-+-"), "-+")
  hline <- str_c("+=", str_c(laply(w, str_dup, string='='), collapse="=+="), "=+")
  endl <- '\n'
  
  cat(line,endl)
  cat(pf(cn), endl)
  cat(hline, endl)
  a_ply(m, 1, function(x){
    cat(pf(x), endl)
    cat(line, endl)
  })
  invisible(df)
}

This functionality is already available in the excellent package ascii. You can see it by comparing the output of mdgridtable(df) with

library(ascii)
print(ascii(df, include.rownames = FALSE), type = 'rest')