# Repeating table calculations using pairs of columns

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Wendy Cameron on 9 May 2018
Commented: Wendy Cameron on 18 May 2018
I have a table of data and need to do repeat calculations using two columns at a time. One of the columns is always the same (DOY), the other column changes across the spreadsheet. How can I do this without just doing them pair by pair. I am trying to predict a value based on a fitted straight line equation between 2 points. My code is: id1=find(isnan(x)); id2 =find(isnan(y)); x([id1,id2])=[] y([id1, id2])=[] p=polyfit(x,y,1) u=polyval(p,12)
An example of the data is attached. I am ne to MATLAB so if you have other better suggestions I'd be very happy to hear them!

Peter Perkins on 14 May 2018
It's likely this can be solved using varfun. That takes a function handle and a table and applies the function to each variable in the table. You can tell it which variables in the table to work on (all but the DoY), and you can give it a function handle that uses your DoY variable. something like
t2 = varfun(@(x) myfun(x,t1.DoY), t1, 'InputVariables',2:end)
(assuming DoY is the first variable in t1.
Wendy Cameron on 18 May 2018
Thank you very much, that has it explained it very clearly. I can imagine a lot of applications for this.