table.concat and table.condense

[Phoenix]

I've rewritten table.concat, making use of a new function I wrote. This allows you to have a nil value in your table, such as

display(stuff)
table {
1: 5
2: 50
3: 52
8: 31
}

In the above, notice keys 4 - 7 are nil. We can either make use of table.condense to rewrite this table, or we can make it simply return the condensed form without rewriting. The new table.concat makes use of it without rewriting.

table.concat (table [, sep [, i [, j [,skiptable]]]])
Given an array where all elements are strings, numbers, OR NIL, returns table..sep..table[i+1] ··· sep..table[j], skipping the nil values. The default value for sep is the empty string, the default for i is 1, and the default for j is the length of the table. If i is greater than j, returns the empty string. If skiptable is true, tables will be skipped instead of generating an incorrect type error. Default for skiptable is true.

table.condense(table [,rewrite])
Given a table, it will condense it to the correct form for an ipairs to handle. If rewrite is true, it will rewrite it to the table. If rewrite is false, it will return the condensed form. The default for rewrite is true.

Code: [show] | [select all] lua

function table.concat(tab,del,min,max,skiptable)
	--these check to make sure the arguments are correct.
	assert(type(tab) == "table", 
	"Bad argument #1 to 'concat'. (table expected, got "..type(tab)..")")		
	assert(type(del) == "string" or type(del)== "nil" or type(del)=="number", 
		"Bad argument #2 to 'concat'. (string expected, got "..type(del)..")")
	assert(type(min) == "number" or type(min)=="nil", 
		"Bad argument #3 to 'concat'. (number expected, got "..type(min)..")")
	assert(type(max) == "number" or type(max)=="nil", 
		"Bad argument #4 to 'concat'. (number expected, got "..type(max)..")")
	if type(skiptable) ~= "boolean" then skiptable = true end
	local tab = table.condense(tab, false)
	local concated = nil 
	local del = del or ""
	local min = min or 1
	max = max or #tab 
	for key,val in ipairs(tab) do
		local typ = type(tab[key])
		if key>=min and key<=max then
			if typ == "string" or typ=="number" or typ=="nil" then
				if tab[key]~=nil then
				concated = (not concated and val) or (concated .. del .. val)
				end
			elseif not skiptable then
				error("invalid value ("..typ..") at index "..key..[[ in 
                                       table for 'concat']])
			end
		end
	end
	return concated or ""
end

Code: [show] | [select all] lua

function table.condense(tab,rewrite)
--this function condenses a tables numerical keys into the lowest it can.
--note, if rewrite is false, it will just return the condensed form. It will not rewrite the table.
--initiation of variables
        if type(rewrite) ~="boolean" then rewrite = true end
        local condensing = {}
        assert(type(tab) == "table", 
                "Bad item to 'condense'. (table expected, got "..type(tab)..")")
--part to get all the numeric pairs off.
        for key,value in pairs(tab) do 
                if type(key)=="number" then 
                        condensing[#condensing+1]=tab[key]
                        if rewrite then tab[key]=nil end
                end
        end
--part to stick them back in.
        if rewrite then
                for i=1,#condensing do 
                        tab[i]=condensing[i]
                end
        else
                 return condensing
        end
end 

A small function to test condense and concat:

Code: [show] | [select all] lua

function testIt()
stuff = {}
stuff[1]="3"
stuff[4]="hi"
stuff[6]=10

echo("NEW CONCAT!")
echo(table.concat(stuff))
 
echo("\nBefore Condense")
for i,x in pairs(stuff) do
echo("\n"..i.." , "..x)
end
 
table.condense(stuff)

echo("\nAfter Condense!")
for i,x in ipairs(stuff) do
echo("\n"..i.." , "..x)
end
end

the old table.concat would display: '3'
The new table.concat would display: '3hi10'

[Rakon]

table.concat does not join two tables, it joins the values in table into a STRING.

Code: [show] | [select all] lua

table.concat({"test","test1","test2"},", ")

Code: Select all

test, test1, test2

Lua Tables
First section is table.concat().
More on Tables



I would advise (if this is still what you want to do) to use an explicitly non-index format for your tables; ie Key,values.

Code: [show] | [select all] lua

testTbl = {}

testTbl['one'] = 1
testTbl['two'] = 2
testTbl['three'] = 3

Above would then be a table :
{['one']= 1, ['two'] = 2, ['three'] = 3}

Please note, table.concat will NOT join two tables, nor will it join table within a table, to the string.

To join a table (depending on your design implemntation) look at the Mudlet functions:
table.intersection()
table.n_intersection()

table.complement()
table.n_complement()

[Phoenix]

this -is- joining a single table into a string.

[Phoenix]

I've edited the original post to have an explanation of the functions used now. Note, with these functions, you've simply got a more robust form of table.concat then otherwise. It'll do the -exact- same stuff... plus a few things. It won't error out on a table by default, it'll just skip it. It will skip nil values instead of erroring, achieving this (in part) by condensing the table prior to concatenation.