Length consecutive value 1 within a 2D matrix

Try this: I've made it general and put the results into a cell array in case some row has more than one region of 1's, like it might have 2 or 5 or 20 runs of 1's.

m = [   0, 0, 0,1,1,1,2 ;
    0,0,1,1,1,1,2;
    0,1,1,1,1,1,0;
    0,0,0,1,1,0,0;
    1,1,0,1,1,1,0] % Last row has 2 contiguous regions instead of 1.
mb = m == 1
[rows, columns] = size(mb);
for row = 1 : rows
    % Make measurements of all lines of 1's.
    props = regionprops(mb(row, :), 'Area');
    % Extract all the lengths into a vector and then put into a cell.
    R{row} = [props.Area];
end
R % Shows in command window

R =

1×5 cell array

{[3]} {[4]} {[5]} {[2]} {[2 3]}

If you know in advance that there is just one run of 1's per row then you can use just a regular (non-cell array) vector:

m = [   0, 0, 0,1,1,1,2 ;
    0,0,1,1,1,1,2;
    0,1,1,1,1,1,0;
    0,0,0,1,1,0,0] % Last row has 2 contiguous regions instead of 1.
mb = m == 1
[rows, columns] = size(mb);
for row = 1 : rows
    % Make measurements of all lines of 1's.
    props = regionprops(mb(row, :), 'Area');
    % Extract all the lengths into a vector and then put into a cell.
    R(row) = [props.Area];
end
R