How to convert cell array to double?

I have U like that :

U =

1×2 cell array

[1×2 double] [1×2 double]

>> U{1}

ans =

1 2

>> U{2}

ans =

2 3

I want to extract value of U and put them in an array sitem= [ ] without duplicate value

Answer 1

[Stephan]

c = {[1 2],[2 3]}
s = cell2mat(c)
s = unique(s)