There is nothing about the code you have shared that would prohibit you from using diff. For some reason, it is not on your MATLAB path. You may need to reset your path using restoredefaultpath
x1 = [98.00 97.68 97.75 98.32 221.00 220.99 221.32 221.32 344.00 343.99 344.33 344.25]';
xdiff=abs(diff(x1))
Not sure what typical values will be. You could use discretize or histcounts to bin your data. Here's one approach assuming your data is sorted.
% use xdiff to determine
nbins = sum(xdiff>mean(xdiff))+1
[N,edges,bin] = histcounts(x1,nbins)
splitapply(@mean,x1,bin)
