How to join particular elements from 2 different lists

See, honestly, list of list is something that is simply just not possible on Appian. The only function that can make it work is merge but instead of this, I would recommend going with a list of dictionaries and cast this to a dictionary. Something like this. 

{
    {
        list: 1,1
    },
    {
        list: 2,1
    },
    {
        list: 3,1
    },
    {
        list: 4,1
    }
}

It is much easier to work and operate on!

See, honestly, list of list is something that is simply just not possible on Appian. The only function that can make it work is merge but instead of this, I would recommend going with a list of dictionaries and cast this to a dictionary. Something like this. 

{
    {
        list: 1,1
    },
    {
        list: 2,1
    },
    {
        list: 3,1
    },
    {
        list: 4,1
    }
}

It is much easier to work and operate on!