Linear Interpolation with few data points

[powersize]

Have another question:

I want to replicate =FORECAST() formula from Excel which does linear interpolation.

Here is my example:

Column X Column Y
X= 1; Y=3
X=1.4; Y=?
X=2 ; Y=4

Y value for 1.4 should be 3.4. If I use Missing Value Note and select Linear Interpolation it retrieves 3.5 which is a simple average of available values in column Y and it does not take into account values in column X. Is there a way to obtain 3.4 value? Linear Regression Predictor does not work here.

Thank you

[AlexanderFillbrunn]

Hi,
Indeed the Linear Regression Learner seems to have problems with such few datapoints. If you really only have 2 known rows, you can easily calculate it yourself, though.
If in your example x1 = 1, y1 = 3, x2 = 2, y2 = 4, x = 1.4, and y = ? you can derive a formula for y:

(x2 - x1) / (y2 - y1) = (x - x1) / (y - y1)   | bring y to one side
(x - x1) * (y2 - y1) / (x2 - x1) + y1 = y

This formula you can use to calculate y for arbitrary x. What you need to do for that, though, is to Unpivot the table, then transpose it, then turn the values into flow variables. Then you can use a Math Formula node for the interpolation. The workflow for it is a bit longer than I would have liked, but pretty straight-forward. Please have a look here. Let me know if you have any questions!
Kind regards,
Alexander

[powersize]

That is exactly it. Thank you Alexander