Hi @DavidS Thanks for reaching out about this! It doesn't seem like it's currently possible to set the new row data based on other columns 
I'd recommend working around this by using a form to add the new data. If you still want the functionality to be a part of the table component, you could follow the suggestion that I made here: http://community.retool.com/t/add-row-window-starts-out-too-low-for-json-column-editor-to-render-correctly/17411