This gist contains useful functions for lua tables inspired directly from the JavaScript documentation.

table-utils.lua

function table.every(self, predicate)
    for key, value in next, self do
        if not predicate(value, key) then
            return false
        end
    end

    return true
end

function table.map(self, predicate, ordered)
    local t = {}

    for k, v in next, self do
        local value = predicate(v, k)

        if not ordered then
            t[k] = value
        else
            table.insert(t, value)
        end
    end

    return t
end

function table.filter(self, predicate, ordered)
    local t = {}

    for key, value in next, self do
        if predicate(value, key) then
            if not ordered then
                t[key] = value
            else
                table.insert(t, value)
            end
        end
    end

    return t
end

function table.extend(self, t, ordered)
    if ordered then
        return { table.unpack(self), table.unpack(t) }
    else
        local newT = {}

        for k, v in next, self do
            newT[k] = v
        end
        
        for k, v in next, t do
            newT[k] = v
        end

        return newT
    end
end

function table.find(self, predicate)
    for key, value in next, self do
        if predicate(value, key) then
            return value
        end
    end

    return nil
end

function table.contains(self, value)
    for _, v in next, self do
        if v == value then
            return true
        end
    end

    return false
end

function table.hasKey(self, key)
    return self[key] ~= nil
end

function table.length(self)
    local mt = getmetatable(self)

    if mt ~= nil and mt.__len ~= nil then
        return mt:__len()    
    end

    local count = 0
    for _, _ in next, self do
        count = count + 1
    end
    return count
end

function table.freeze(self)
    return setmetatable({}, {
        __index = function(_, key)
            return self[key]
        end,

        __newindex = function(_, key, value)
            error(("Cannot set property '%s' to '%s', table is frozen"):format(key, tostring(value)))
        end,

        __len = function()
            return table.length(self)
        end
    })
end