How to plot only positive values?

I have a function y=f(x) where 'x' varies within a particular range. For some values of 'x', 'y' gives positive values whereas for some other values 'y' gives negative values. I have two questions:

1.. I have written a table as;

T=table(x,y);
writetable(T,'table.txt');

How can I get a table for only the positive values of 'y' and their corresponding 'x' values?

2.. Using the plot command (without using the table), how can I get a plot for only the positive values of 'y' and their corresponding 'x' values?

Thanks.

Answer 1

[Jakob B. Nielsen]

You can use logical indexing.

posY=Y(Y>0); 
posX=X(Y>0); %the X values for which it is true that the value of Y in the corresponding index is greater than 0. 

After that, it is simple to plot(posX,posY);