code: def histogram_multiple(numberfiles, vmin, vmax, xlabel, title, outfmt="pdf",
                         tags=None, bins=20, skip=0, ascii=False,
                         facet=False, fill="white", prefix=""):
      
      if ascii:
          return texthistogram(numberfiles, vmin, vmax, title=title,
                  bins=bins, skip=skip)
  
      newfile = "_".join(op.basename(x).split(".")[0] for x in numberfiles)
  
      fw = open(newfile, "w")
      print("{0}\tgrp".format(xlabel), file=fw)
  
      if tags:
          tags = tags.split(",")
  
      for i, f in enumerate(numberfiles):
          data, va, vb = get_data(f, vmin, vmax, skip=skip)
          vmin = min(vmin, va)
          vmax = max(vmax, vb)
  
          fp = open(f)
          if tags:
              tag = tags[i]
          else:
              tag = op.basename(f).rsplit(".", 1)[0]
          for row in fp:
              val = row.strip()
              print("\t".join((val, tag)), file=fw)
      fw.close()
  
      numberfile = newfile
      outfile = numberfile + '.' + outfmt
      if prefix:
          outfile = prefix + outfile
      htemplate = histogram_multiple_template_b \
                      if facet else histogram_multiple_template_a
      rtemplate = RTemplate(htemplate, locals())
      rtemplate.run()
docs: Generate histogram using number from numberfile, and only numbers in the
      range of (vmin, vmax). First combining multiple files.