How to use math.random w/ in pairs?

The pairs function returns all the keys and values of the argument table, math.random returns a random integer. For this reason, you can't directly index a value at a non-integer key with a value generated from math.random. Here's a potential workaround:

function obtainRandomKeyValuePair(tab)
    local randIndex = math.random(1, #tab);
    local curIndex = 1;

    for k, v in pairs(songs) do
        if curIndex >= randIndex then
            return k, v;
        end

        curIndex = curIndex + 1;
    end
end

You would then call the function with:

local key, val = obtainRandomKeyValuePair(songs);

EDIT: Apparently the length operator doesn't work on tables with non-numeric indices. That's really poor design. At any rate, I would switch to a 2D table. Here's an example:

local songs = {
    titles = {
        "Friday",
        "The Song of the Cebu",
        "Problem",
        "Bills"
    },
    ids = {
        "268763467",
        "142570249",
        "261244793",
        "165508381"
    }
};

local randIndex = math.random(1, #songs.titles);
local title = songs.titles[randIndex];
local id = songs.ids[randIndex];