row-oriented-workflows | Row-oriented workflows in R with the tidyverse

Here's my solution. This problem is not really a purrr task, because there is nothing really that you want to map a single function to. Instead, what I understand the problem to be is that you want to match each X value in a Bounce row with the corresponding Smooth row X values of the same Date and Seq1 (and there is only one such row). This means that it is really a merging or joining problem, and then the approach is to set up the join so that you can match the right values and do the sum. So I go as follows:

1. Split the data into the Smooth rows and the Bounce rows and gather so that all the X values are in one column
2. Join the smooths onto the bounces with a left_join, so each original Bounce row now has its corresponding Smooth.
3. mutate the sum into a new column and select/rename the columns to be as in the original
4. bind_rows to join the newly summed bounces and spread to return to the original layout.

This should be robust to any number of Date, Seq1, Seq2 and X values.