[suicidalkatt]

Originally Posted by elcius lua has no problem with very large tables, just make an itemid to setid lookup table. ~ Snip

While your method would be ideal, it doesn't really do what the author intended.

I believe they want to have the tooltip show every set that contains a particular itemID not just the first one that returns true.

local setName =  {
[1] = {  name = "Mystic's Regalia (Recolor)", items = {14090, 26008, 14094}, },
-- [2......1778]
[1779] = {  name = "Imperial Plate", items = {31436, 30002, 12424, 12425, 12422, 12427, 12429}, },
}
 
-- make lookup table, this will create a list that looks something like this
--[[
local table = {
    [14090] = {201,560,888} -- Item id = Table of setName[index] values
}
]]
local itemSet = {}
do 
    for i,set in pairs(setName) do -- Looks through all the set
        for j, id in pairs(set['items']) do -- looks though just the items table within
            if not itemSet[id] then itemSet[id] = {} end -- creates a table within itemSet for each id (only once)
            tinsert(itemSet[id], i) -- inserts each set index into the table
        end
    end
end
 
function addline_gametip()
    local itemName,itemLink = GameTooltip:GetItem();
    if not itemLink then return end
    
    local itemId = tonumber(itemLink:match('item:(%d+)'));
    if itemSet[itemId] then -- if a set is found
        for i, setIndex in pairs(itemSet[itemId]) do -- for each index the id has
            GameTooltip:AddLine("Transmog Set: " .. setName[setIndex]['name']); -- add a line to the game tooltip
        end
    end
 end
 
 
GameTooltip:HookScript("OnTooltipSetItem", addline_gametip);