function! SortByCurrent(b1, b2)
  return a:b1['current'] == a:b2['current'] ? 0 : a:b1['current'] < a:b2['current'] ? 1 : -1
endfunction

function! SortByAlternate(b1, b2)
  return a:b1['alternate'] == a:b2['alternate'] ? 0 : a:b1['alternate'] < a:b2['alternate'] ? 1 : -1
endfunction

function! GetBufferList()
  redir => bufliststr
  silent! ls
  redir END

  let bufferlist = split(bufliststr, '\n')
  " For loop as requested.
  "for i in range(0, len(bufferlist) - 1)
  "  let bufferlist[i] = substitute(bufferlist[i], '^\s*\(\d\+\)\(\s*[-u%#ah=+x ]*\)\s\+\(\".\{-}\"\)\s\+line\s\+\(\d\+\)\s*$', '\1,\2,\4,\3','g')
  "endfor

  "I'm stubborn, so I used double single quotes to avoid the backslashitis,
  "but feel free to use the for loop :p
  call map(bufferlist,
        \'substitute(v:val,'.
        \'''\m\C^\s*\(\d\+\)\(\s*[-u%#ah=+x ]*\)\s\+"\(.\{-}\)"\s\+line\s\+\(\d\+\)\s*$'','.
        \'''\1,\2,\4,\3'',''g'')')
  " Split on commas (I know)
  call map(bufferlist, 'split(v:val, ",")')
  " Restore file names with comma(s)
  call map(bufferlist, 'add(v:val[0:2], join(v:val[3:-1], ","))')
  " Added entries for the other flags.
  " Empty names give an empty string instead of "[No Name]".
  call map(bufferlist,
        \ '{"number": v:val[0],'
        \.'"line": v:val[2],'
        \.'"name": (v:val[3] =~ ''\[.\{-}\]'' ? bufname(v:val[0]) : v:val[3]),'
        \.'"listed": v:val[1] !~ "u",'
        \.'"current": v:val[1] =~ "%",'
        \.'"alternate": v:val[1] =~ "#",'
        \.'"active": v:val[1] =~ "a",'
        \.'"hidden": v:val[1] =~ "h",'
        \.'"modifiable": v:val[1] !~ "-",'
        \.'"readonly": v:val[1] =~ "=",'
        \.'"modified": v:val[1] =~ "+",'
        \.'"read_error": v:val[1] =~ "x"}')

  " Is filtering faster than sorting?
  "let current = sort(copy(bufferlist), 'SortByCurrent')[0]['number']
  "let alternate = sort(copy(bufferlist), 'SortByAlternate')[0]['number']
  let current = filter(copy(bufferlist), 'v:val["current"] == 1')[0].number
  let alternate_l = filter(copy(bufferlist), 'v:val["alternate"] == 1')
  let alternate = len(alternate_l) > 0 ? alternate_l[0].number : ''
  return {'list': bufferlist, 'current': current, 'alternate': alternate}
endfunction

echo GetBufferList()