I would recommend a combination of the Window transform and FILL function, which allows you to fill with the value in the preceding row.
To do this, please follow the instruction below,
- Add a new step
- type "Window" for the transformation
- Under "Formula," type "fill" for the fill function. Enter the column of interest as the argument.
- Under "Order By," enter "sourcerownumber()" if you like the order as it is.
Click on the following links for more details,
https://www.trifacta.com/support/articles/article/473170-faq-window-functions/