I am curious how JMP organizes data with the Group X function. For this example:
Does JMP simply create groups based on the number of data points?
because your X grouping column is continuous JMP divides the groupings into equal number groups. If the column was ordinal or nominal it would create a grouping for each value found for the column.
For a continuous column in either the Group X or Group Y role, JMP uses quantiles to divide the data into 5 groups.
As Ian@JMP points out, you can right click on the grouping variable label and select Number of Levels to change how many groups are created (still based on quantiles).