Table Utils

wiki

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 ) )

Print a table recursively

ISSUE: this should return a string rather than assume how the user wants to output the text.

-- Print anything - including nested tables
function table_print (tt, indent, done)
  done = done or {}
  indent = indent or 0
  if type(tt) == "table" then
    for key, value in pairs (tt) do
      io.write(string.rep (" ", indent)) -- indent it
      if type (value) == "table" and not done [value] then
        done [value] = true
        io.write(string.format("[%s] => table\n", tostring (key)));
        io.write(string.rep (" ", indent+4)) -- indent it
        io.write("(\n");
        table_print (value, indent + 7, done)
        io.write(string.rep (" ", indent+4)) -- indent it
        io.write(")\n");
      else
        io.write(string.format("[%s] => %s\n",
            tostring (key), tostring(value)))
      end
    end
  else
    io.write(tt .. "\n")
  end
end

Universal tostring

function table_print (tt, indent, done)
  done = done or {}
  indent = indent or 0
  if type(tt) == "table" then
    local sb = {}
    for key, value in pairs (tt) do
      table.insert(sb, string.rep (" ", indent)) -- indent it
      if type (value) == "table" and not done [value] then
        done [value] = true
        table.insert(sb, "{\n");
        table.insert(sb, table_print (value, indent + 2, done))
        table.insert(sb, string.rep (" ", indent)) -- indent it
        table.insert(sb, "}\n");
      elseif "number" == type(key) then
        table.insert(sb, string.format("\"%s\"\n", tostring(value)))
      else
        table.insert(sb, string.format(
            "%s = \"%s\"\n", tostring (key), tostring(value)))
       end
    end
    return table.concat(sb)
  else
    return tt .. "\n"
  end
end

function to_string( tbl )
    if  "nil"       == type( tbl ) then
        return tostring(nil)
    elseif  "table" == type( tbl ) then
        return table_print(tbl)
    elseif  "string" == type( tbl ) then
        return tbl
    else
        tostring(tbl)
    end
end

Example

print(to_string{
  "Lua",user="Mariacher",
  {{co=coroutine.create(function() end),{number=12345.6789}},
   func=function() end}, boolt=true} )

This prints

"Lua"
{
  {
    {
      number = "12345.6789"
    }
    co = "thread: 0212B848"
  }
  func = "function: 01FC7C70"
}
boolt = "true"
user = "Mariacher"

See Also: LuaRecipes - Recursive table print/serialization

Count item occurances 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

Explode string into table with seperator

-- explode(seperator, string)
function explode(d,p)
  local t, ll
  t={}
  ll=0
  if(#p == 1) then return p end
    while true do
      l=string.find(p,d,ll+1,true) -- find the next d in the string
      if l~=nil then -- if "not not" found then..
        table.insert(t, string.sub(p,ll,l-1)) -- Save it in our array.
        ll=l+1 -- save just after where we found it for searching next time.
      else
        table.insert(t, string.sub(p,ll)) -- Save what's left in our array.
        break -- Break at end, as it should be, according to the lua manual.
      end
    end
  return t
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

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