Start / Stop Values ​​for Sequential Number Blocks

Question

If I have a vector:

[4,5,6,7,11,12,13,14,21,22,23]

How can I extract the start / end values ​​of all consecutive numeric blocks without a loop, i.e. the desired result for the above vector will be a two-column vector:

b = 

4   7
11  14
21  23

Answer 1

Easily:

a = [4,5,6,7,11,12,13,14,21,22,23];
b = reshape(a(sort([find(a - circshift(a,[0,1]) ~= 1),find(a - circshift(a,[0,-1]) ~= -1)])),2,[])'

Output:

b =

 4     7
11    14
21    23

Answer 2

Another approach:

x = [4,5,6,7,11,12,13,14,21,22,23];
x = x(:);
ind = find([1; diff(x)-1; 1]);
result = [x(ind(1:end-1)) x(ind(2:end)-1)];

Answer 3

:

    v  = [4,5,6,7,11,12,13,14,21,22,23];

    dv = diff(diff(v)==1);

    bv = find(dv==+1)+1;
    if dv(1) == 0
            bv = [1,bv];
    end;

    ev = find(dv==-1)+1;
    if dv(end) == 0
            ev = [ev,numel(v)];
    end;

    b = v([bv(:),ev(:)]);

Answer 4

, , , :

x = (0:10:a(end))'; %'
subindex = @(A) [A(1) A(end)];
fun = @(q) subindex( a(a>q & a<q+10));
res = cell2mat(arrayfun(fun, x, 'UniformOutput', false));

a.