I'm correcting myself, the abs MUST be changed to fabs

did you really needed to use lambda?
you could just return std::abs(a - b) < 1e-3;

it was better to use const auto& i in the range based loop for speed optimizations instead of creating strings in the vector size for the real strings data! but the approach can be considered as mature enough

consexpr benefits only if the past function will be executed with known value at compile time, but nice idea
+1

you may not print extra stuff to stdout if your function was not sopused to! instead you can throw exception if you want to, or set error code