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History of Idiom 26 > diff from v28 to v29

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Version 28

2016-04-07, 06:44:10

Version 29

2016-04-07, 09:37:34

Idiom #26 Create a 2-dimensional array

Declare and initialize a matrix x having m rows and n columns, containing real numbers.

Idiom #26 Create a 2-dimensional array

Declare and initialize a matrix x having m rows and n columns, containing real numbers.

Code 
local array = setmetatable({},{
   __index = function(t1,k1)
      t1[k1] = setmetatable({},{
         __index = function(t2,k2)
            t2[k2] = 0
            return t2[k2]
         end
      })
      return t1[k1]
   end
})
Code 
local array = setmetatable({},{
   __index = function(t1,k1)
      t1[k1] = setmetatable({},{
         __index = function(t2,k2)
            t2[k2] = 0
            return t2[k2]
         end
      })
      return t1[k1]
   end
})
Comments bubble
2D array are table of table (table are hashmap).

Use metatable to lazy initialize each row (t1[k1]) and each column (t2[k2]) the first time it's accessed.
Comments bubble
2D array are table of table (table are hashmap).

Use metatable to lazy initialize each row (t1[k1]) and each column (t2[k2]) the first time it's accessed.

see http://www.programming-idioms.org/idiom/27/create-a-3-dimensional-array/1675/lua for a more "standard" way
Doc URL
http://www.lua.org/pil/11.2.html
Doc URL
http://www.lua.org/pil/11.2.html
Demo URL
http://codepad.org/KUJ0koqr
Demo URL
http://codepad.org/KUJ0koqr