c++ - Is there an STL algorithm to find if an element is present in a container based on some tolerance? -

the problem trying solve following: have container of floating points (vector of double vectors):

std::vector<std::vector<double>> dv { {0.0, 0.0}, {1.0, 0.0}, {0.0, 1.0}, {1.0, 1.0} }; 

then, assume have new point (double vector):

std::vector<double> v1 {0.0001, 1.0}; 

i want check if point v1 present in dv container based on tollerance. distance between 2 vectors calculated euclidean distance.

i have looked relevant questions , answers:

• how find if item present in std::vector?
• check if std::vector contains object?

and trying use std::find_if() without success, accepts unary predicate.

at moment came temporary solution. first, created generic function find euclidean distance between 2 vectors:

template <typename inputit1, typename inputit2> double euclideandistance(inputit1 beg1, inputit1 end1, inputit2 beg2) {   double val = 0.0;   while (beg1 != end1) {     double dist = (*beg1++) - (*beg2++);     val += dist*dist;   }   return val > 0.0? sqrt(val) : 0.0; } 

second, created check_if function check if element presented in container based on tolerance (epsilon):

template <typename container, typename element> bool check_if(const container& c, const element& el,               const double epsilon = 0.001) {   auto pos = c.begin();   (; pos != c.end(); ++pos) {     if (euclideandistance(pos->begin(), pos->end(), el.begin()) < epsilon) {       return true;     }   }   return false; } 

and can use code in context this:

// check if container contains v1 using check_if() if (check_if(dv, v1)) {   std::cout << "using check_if() - container contains v1\n"; } 

so questions following:

1. is there in-house stl algorithm achieve same goal? if no, how improve code? example, i'm not sure how use distance function in check_in() instead of euclideandistance()?
2. i wonder if ashleysbrain suggestion (https://stackoverflow.com/a/3451045/3737891) use std::set instead of std::vector make difference having container of floating points?

and trying use std::find_if() without success, accepts unary predicate.

that's want anyway. single argument going elements of vector you're looking in.

std::vector<std::vector<double>> dv{     {0.0, 0.0}, {1.0, 0.0}, {0.0, 1.0}, {1.0, 1.0}};  std::vector<double> v1 {0.0001, 1.0};  auto find_result =     std::find_if(begin(dv), end(dv), [&v1](std::vector<double> const &dve) {       assert(dve.size() == v1.size());       return euclideandistance(begin(dve), end(dve), begin(v1)) < 0.001;     }); 

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on note, if points fixed dimension using vector<double> not right representation. tuple<double,double>, or array<double 2>, or custom class has overloaded operators appropriate replacements.