Table Utils

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Convert a table to a string

Produces a compact, uncluttered representation of a table. Mutual recursion is employed.

function table.val_to_str ( v )
 if "string" == type( v ) then
 v = string.gsub( v, "\n", "\\n" )
 if string.match( string.gsub(v,"[^'\"]",""), '^"+$' ) then
 return "'" .. v .. "'"
 end
 return '"' .. string.gsub(v,'"', '\\"' ) .. '"'
 else
 return "table" == type( v ) and table.tostring( v ) or
 tostring( v )
 end
end
function table.key_to_str ( k )
 if "string" == type( k ) and string.match( k, "^[_%a][_%a%d]*$" ) then
 return k
 else
 return "[" .. table.val_to_str( k ) .. "]"
 end
end
function table.tostring( tbl )
 local result, done = {}, {}
 for k, v in ipairs( tbl ) do
 table.insert( result, table.val_to_str( v ) )
 done[ k ] = true
 end
 for k, v in pairs( tbl ) do
 if not done[ k ] then
 table.insert( result,
 table.key_to_str( k ) .. "=" .. table.val_to_str( v ) )
 end
 end
 return "{" .. table.concat( result, "," ) .. "}"
end

Example:

t = {['foo']='bar',11,22,33,{'a','b'}}
print( table.tostring( t ) )

This prints {11,22,33,{"a","b"},foo="bar"} .

Recursive table print/stringification/serialization =

See TableSerialization.

Count item occurrences in table

-- Count the number of times a value occurs in a table 
function table_count(tt, item)
 local count
 count = 0
 for ii,xx in pairs(tt) do
 if item == xx then count = count + 1 end
 end
 return count
end

Remove duplicates from table

-- Remove duplicates from a table array (doesn't currently work
-- on key-value tables)
function table_unique(tt)
 local newtable
 newtable = {}
 for ii,xx in ipairs(tt) do
 if(table_count(newtable, xx) == 0) then
 newtable[#newtable+1] = xx
 end
 end
 return newtable
end

Randomly sample from List

RandomSample has a better algorithm but it has the same issue with math.random

-- Careful of random number seeding here- you will need to randomly
-- seed before calling this
function randomlist(l, samp)
 local newlist
 newlist = {}
 if not samp then 
 samp = 0 
 else
 samp = #l - samp
 end
 while #l > samp do
 local idx
 idx = math.random(1, #l)
 newlist[#newlist + 1] = l[idx]
 table.remove(l, idx)
 end
 return newlist
end

Implode table into string with separator

ISSUE: Users should use built-in fn table.concat(table,divider)

-- implode(separator, table)
function implode(d,p)
 local newstr
 newstr = ""
 if(#p == 1) then
 return p[1]
 end
 for ii = 1, (#p-1) do
 newstr = newstr .. p[ii] .. d
 end
 newstr = newstr .. p[#p]
 return newstr
end

Generate combinations from list

-- combo({a,b,c},2) ==> a,b a,c b,c
-- an iterating solution would be appreciated too
function combo(lst, n)
 local a, number, select, newlist
 newlist = {}
 number = #lst
 select = n
 a = {}
 for i=1,select do
 a[#a+1] = i
 end
 newthing = {}
 while(1) do
 local newrow = {}
 for i = 1,select do
 newrow[#newrow + 1] = lst[a[i]]
 end
 newlist[#newlist + 1] = newrow
 i=select
 while(a[i] == (number - select + i)) do
 i = i - 1
 end
 if(i < 1) then break end
 a[i] = a[i] + 1
 for j=i, select do
 a[j] = a[i] + j - i
 end
 end
 return newlist
end

Generate combinations from list - Iterator version

Should be faster for large t and n as it updates only the items that change from combo to combo, instead of recreating the combo row each iteration.

By RichardWarburton.

function combo(t,n)
 local n,max,tn,output=n,#t,{},{}
 for x=1,n do tn[x],output[x]=x,t[x] end -- Generate 1st combo
 tn[n]=tn[n]-1 -- Needed to output 1st combo
 return function() -- Iterator fn
 local t,tn,output,x,n,max=t,tn,output,n,n,max
 while tn[x]==max+x-n do x=x-1 end -- Locate update point
 if x==0 then return nil end -- Return if no update point
 tn[x]=tn[x]+1 -- Add 1 to update point (UP)
 output[x]=t[tn[x]] -- Update output at UP
 for i=x+1,n do 
 tn[i]=tn[i-1]+1 -- Update points to right of UP
 output[i]=t[tn[i]] -- Update output to refect change in points
 end
 return output
 end
end

Insert values from one table into another table

--DavidManura

-- tinsertvalues(t, [pos,] values)
-- similar to table.insert but inserts values from given table "values",
-- not the object itself, into table "t" at position "pos".
-- note: an optional extension is to allow selection of a slice of values:
-- tinsertvalues(t, [pos, [vpos1, [vpos2, ]]] values)
-- DavidManura, public domain, http://lua-users.org/wiki/TableUtils
function tinsertvalues(t, ...)
 local pos, values
 if select('#', ...) == 1 then
 pos,values = #t+1, ...
 else
 pos,values = ...
 end
 if #values > 0 then
 for i=#t,pos,-1 do
 t[i+#values] = t[i]
 end
 local offset = 1 - pos
 for i=pos,pos+#values-1 do
 t[i] = values[i + offset]
 end
 end
end
--[[ tests:
 local t = {5,6,7}
 tinsertvalues(t, {8,9})
 tinsertvalues(t, {})
 tinsertvalues(t, 1, {1,4})
 tinsertvalues(t, 2, {2,3})
 assert(table.concat(t, '') == '123456789')
--]]

Iterate over the non-ipairs keys in a table

See LuaList:2010-12/msg01143.html ("hpairs" discussion).

Comments

Maybe rename this to TableRecipes? (like StringRecipes).

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Last edited January 2, 2011 8:31 am GMT (diff)