Select all Rows that Contain A Certain Number and Any NaN's That follow Them

I have a 94x4 matrix. A truncated example is below:

A = 
434.390000000000	1	NaN	NaN
434.700000000000	NaN	NaN	42.0570000000000
434.760000000000	1	NaN	NaN
438.720000000000	NaN	NaN	46.6870000000000
441.640000000000	16	NaN	NaN
441.720000000000	NaN	NaN	46.3582500000000
447.250000000000	NaN	NaN	39.7590000000000
453.590000000000	NaN	NaN	39.3142500000000
556.390000000000	1	NaN	NaN
558.880000000000	NaN	NaN	43.4190000000000
562.400000000000	NaN	NaN	39.4925000000000
566.060000000000	NaN	NaN	38.6045000000000
568.430000000000	NaN	NaN	39.5280000000000
573.810000000000	NaN	NaN	37.6187500000000
2009.14000000000	1	NaN	NaN
2010.26000000000	1	NaN	NaN
2010.51000000000	1	NaN	NaN
2011.14000000000	1	NaN	NaN
2013.80000000000	NaN	NaN	39.1890000000000
2019.39000000000	NaN	NaN	36.4470000000000
2020.89000000000	16	NaN	NaN
2021.51000000000	16	NaN	NaN
2023.18000000000	NaN	NaN	36.4445000000000

What I would like to do is select all the rows that contain a 1 in column 2 as well as all the rows that follow the 1's that contain NaN's. From the above example this is what I would want:

B =
434.390000000000	1	NaN	NaN
434.700000000000	NaN	NaN	42.0570000000000
434.760000000000	1	NaN	NaN
438.720000000000	NaN	NaN	46.6870000000000
556.390000000000	1	NaN	NaN
558.880000000000	NaN	NaN	43.4190000000000
562.400000000000	NaN	NaN	39.4925000000000
566.060000000000	NaN	NaN	38.6045000000000
568.430000000000	NaN	NaN	39.5280000000000
573.810000000000	NaN	NaN	37.6187500000000
2009.14000000000	1	NaN	NaN
2010.26000000000	1	NaN	NaN
2010.51000000000	1	NaN	NaN
2011.14000000000	1	NaN	NaN
2013.80000000000	NaN	NaN	39.1890000000000
2019.39000000000	NaN	NaN	36.4470000000000

Any help is much appreciated and I am happy to clarify anything. Thanks!

Answer 1

[TADA]

I think in this case a simple loop will be better than a fancy vectorised solution.

valid = false(size(A, 1),1);
valid(1) = A(1,2) == 1;
for i = 2:size(A, 1)
    curr = A(i,2);
    if curr == 1 || (isnan(curr) && valid(i-1))
        valid(i) = true;
    end
end

B = A(valid,:);