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 is to help with printing tables for use with markdown. I use pandoc to convert markdown to html and it can handle the tables formatted this way.

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')