Instead of insisting on the SankeyMATIC format for specifying flows, allow people to just copy some cells from a spreadsheet and paste them in & get the results they expect.
I believe the right way to support this would be to expect three columns of pasted data.
Figure out which column has the numeric values. Could be column 1 or 2 or 3
Once we know which two columns are not the values, presume the first column of the two is the Source & the second is the Target.
Instead of insisting on the SankeyMATIC format for specifying flows, allow people to just copy some cells from a spreadsheet and paste them in & get the results they expect.
I believe the right way to support this would be to expect three columns of pasted data.