Re: Lua representation of complex tabular data, for use by simulation

[Peter Shook <pshook@...>]

Laritz, Thomas wrote:
> We are developing a C++ simulation which requires complex tabular (as well as scalar and string) data to be read in at the start of execution. These data are read from files.  We'd like to start using Lua syntax to specify these input files.  However, given the varied nature of the tabular data, it seems that there might be many ways (some better than others) to represent this tabular data using Lua's capabilities.  Can anyone, who has faced this problem, share any techniques, examples or SW?  

I find a function name followed by a table record to be the most 
flexible approach.  Then anyone can process your data in Lua, or store 
it in there own C/C++ structures, or store it in a database.  The 
function can check the record, add a class or metatable, and store it 
however and whereever you wish.

I like to store the records in a table as a list.  Then it's easy to 
grep, map and sort the data.

Here is an example:

$ cat data

-- { style   , brand    ,  year,  cost, }

rec{ Economy , Ford     ,  2003,   8.0, }
rec{ Sedan   , Ford     ,  2003,  15.0, }
rec{ Luxury  , Ford     ,  2003,  23.0, }
rec{ Sports  , Ford     ,  2003,  19.0, }
rec{ SUV     , Ford     ,  2003,  26.0, }

rec{ Economy , GM       ,  2003,   7.0, }
rec{ Sedan   , GM       ,  2003,  19.0, }
rec{ Luxury  , GM       ,  2003,  28.0, }
rec{ Sports  , GM       ,  2003,  24.0, }
rec{ SUV     , GM       ,  2003,  28.0, }

rec{ Economy , Chrysler ,  2003,   9.0, }
rec{ Sedan   , Chrysler ,  2003,  14.0, }
rec{ Luxury  , Chrysler ,  2003,  25.0, }
rec{ Sports  , Chrysler ,  2003,  22.0, }
rec{ SUV     , Chrysler ,  2003,  24.0, }

rec{ Economy , Toyota   ,  2003,   7.5, }
rec{ Sedan   , Toyota   ,  2003,  17.0, }
rec{ Luxury  , Toyota   ,  2003,  30.0,   extra = AC }
rec{ Sports  , Toyota   ,  2003,  28.0, }
rec{ SUV     , Toyota   ,  2003,  31.0,   extra = SunRoof }

rec{ Economy , Honda    ,  2003,   8.2, }
rec{ Sedan   , Honda    ,  2003,  18.0, }
rec{ Luxury  , Honda    ,  2003,  29.0,   extra = Leather }
rec{ Sports  , Honda    ,  2003,  32.0, }
rec{ SUV     , Honda    ,  2003,  30.0,   extra = AC }


$ cat ex.lua

local key_index = {
  style = 1,
  brand = 2,
  year  = 3,
  cost  = 4,
}

local defaults = {
  extra = 'none',
}

local rec_mt = {}

function rec_mt.__index(t, k)
  local index = key_index[k]
  if index ~= nil then return t[index] end
  return assert(defaults[k], 'bad key')
end

all_the_data = {}

local sandbox = {}

function sandbox.rec(rt)
  assert(type(rt)=='table', 'record must be a table')
  local style, brand, year, cost = unpack(rt)
  assert(style, 'bad style')
  assert(brand, 'bad brand')
  assert(year,  'bad year')
  assert(cost,  'bad cost')
  setmetatable(rt, rec_mt)
  table.insert(all_the_data, rt)
end

local function lit(names)
  for n in string.gfind(names, '%w+') do sandbox[n] = n end
end

lit'Economy Sedan Luxury Sports SUV' -- styles
lit'Ford GM Chrysler Toyota Honda'   -- brands
lit'AC Leather SunRoof'              -- extras

local f = assert(loadfile('data'))
setfenv(f, sandbox)
f()

function rec_mt.__lt(a, b)
  return a.cost < b.cost
end

table.sort(all_the_data)
print'sorted by cost'
for i,rt in ipairs(all_the_data) do
  io.write(string.format('%-10s %-10s %d %4.1f\n', unpack(rt)))
end
print''

local so = { Economy=1, Sedan=2, Luxury=5, Sports=3, SUV=4 }
local function comp_style_cost(a, b)
  local aso, bso = so[a.style], so[b.style]
  return aso < bso or (aso == bso and a.cost < b.cost)
end

table.sort(all_the_data, comp_style_cost)
print'sorted by style and cost'
for i,rt in ipairs(all_the_data) do
  io.write(string.format('%-10s %4.1f %10s %d %-10s\n',
                         rt.style, rt.cost, rt.brand, rt.year, rt.extra))
end


$ lua ex.lua

sorted by cost
Economy    GM         2003  7.0
Economy    Toyota     2003  7.5
Economy    Ford       2003  8.0
Economy    Honda      2003  8.2
Economy    Chrysler   2003  9.0
Sedan      Chrysler   2003 14.0
Sedan      Ford       2003 15.0
Sedan      Toyota     2003 17.0
Sedan      Honda      2003 18.0
Sports     Ford       2003 19.0
Sedan      GM         2003 19.0
Sports     Chrysler   2003 22.0
Luxury     Ford       2003 23.0
Sports     GM         2003 24.0
SUV        Chrysler   2003 24.0
Luxury     Chrysler   2003 25.0
SUV        Ford       2003 26.0
SUV        GM         2003 28.0
Sports     Toyota     2003 28.0
Luxury     GM         2003 28.0
Luxury     Honda      2003 29.0
Luxury     Toyota     2003 30.0
SUV        Honda      2003 30.0
SUV        Toyota     2003 31.0
Sports     Honda      2003 32.0

sorted by style and cost
Economy     7.0         GM 2003 none
Economy     7.5     Toyota 2003 none
Economy     8.0       Ford 2003 none
Economy     8.2      Honda 2003 none
Economy     9.0   Chrysler 2003 none
Sedan      14.0   Chrysler 2003 none
Sedan      15.0       Ford 2003 none
Sedan      17.0     Toyota 2003 none
Sedan      18.0      Honda 2003 none
Sedan      19.0         GM 2003 none
Sports     19.0       Ford 2003 none
Sports     22.0   Chrysler 2003 none
Sports     24.0         GM 2003 none
Sports     28.0     Toyota 2003 none
Sports     32.0      Honda 2003 none
SUV        24.0   Chrysler 2003 none
SUV        26.0       Ford 2003 none
SUV        28.0         GM 2003 none
SUV        30.0      Honda 2003 AC
SUV        31.0     Toyota 2003 SunRoof
Luxury     23.0       Ford 2003 none
Luxury     25.0   Chrysler 2003 none
Luxury     28.0         GM 2003 none
Luxury     29.0      Honda 2003 Leather
Luxury     30.0     Toyota 2003 AC