rename columns

[adampolcz]

I was able to dynamically select the columns I need but now I need to use a formula tool which makes a new column and its value is based on the last 2 columns. But since I don't know it's names how can I say: get the value of the last column minus the value of the column 2 to the left? 

[binu_acs]

@adampolcz @Can you provide a sample input file and expected result based for better understanding of your use-case

[adampolcz]

I was able to manage this with python tool, thanks!