You should never compare for exact equivalence of floating point numbers, read this to know why:
Always compare the absolute difference of values against a tolerance, like this:
>> data = [0.1,0.50;0.15,0.72;0.2,0.37;0.25,0.18;0.3,0.65]
data =
0.10000 0.50000
0.15000 0.72000
0.20000 0.37000
0.25000 0.18000
0.30000 0.65000
>> val = 0.15;
>> idx = abs(data(:,1)-val)<1e-5;
>> out = data(idx,2)
out = 0.72000
