Changing redux state but also retain some old values of state

In my React-Redux app, I am changing the redux state and it looks something like this

state {
    key1: oldVal1
    key2: oldArray1 //The value here is an array
    .
    .
    .
}

Now when I update the state next time...

state {
    key1: newVal1

    //But for key2 I want to keep the value as the same oldArray1
    //Now since that oldArray1 is not anywhere except in the old state, can I do this...?

    key2: state.key2
    .
    .
    .
}

So if I do key2: state.key2 and state.key2 is an array, will the reference be lost since state is changed and state.key2 won't point to anything?

I just want a rough explanation of how object/array references will affect state in redux.