The syntax
rcs=M(:,4)
will give a one-column table.
The syntax
rcs=M{:,4}
will give a column of data of the class that is stored in the table. I think that's what you want.
filename = 'Book11.csv';
M = readtable(filename);
a=M{:,3};%phi
b=90;
f=unique(M(:,1)); %freq
rcs=M{:,4};
ys = smooth(rcs,10);
plot(a,rcs,'k'); hold on; grid on
plot(a,ys,'r')
legend('original','average')
(I have not tried to solve why you don't get the graph you expected here.)
