Expression node - how to perform logic where are any examples?

I am trying to use the Expression node to perform some logic: I gave split the first name field up if there is a full stop in the firstname.

What I want to do next is delete any fields thats are less than 1 characters in the first split column.

And then what I need help with is how do I compare the columns and perform updates on calculated function.

For example if the Column 1 field is ‘Mr’ then I want to replace it with the Column 2 value, and set the salutation to ‘Mr’