Question

I need a structure to hold a value based on a key that has a range. My implementation is C++, so any STL or Boost would be excellent.

I have as range-key, which are doubles, and value

• [0,2) -> value1
• [2,5) -> value2
• [5,10) -> value3
• etc

Such that a search of 1.23 should return value1, and so on.

Right now I am using a vector containing all three parts, key1/key2/value, with custom searching, but it feels like there should be a cleaner structure.

Edit: Thanks all. Given the ranges in this case are supposed to be contiguous and non-overlapping, the use of upper_bound will work just fine. Thanks for the class Range solutions as well, they are filed away for future reference.

Answer 1

If your ranges are contiguous and non-overlapping, you should use std::map and the upper_bound member function. Or, you could use a sorted vector with the upper_bound algorithm. Either way, you only need to record the lowest value of the range, with the upper part of the range being defined by the next higher value.

Edit: I phrased that confusingly, so I decided to provide an example. In coding the example, I realized you need upper_bound instead of lower_bound. I always get those two confused.

typedef std::map<double, double> MyMap; MyMap lookup; lookup.insert(std::make_pair(0.0, dummy_value)); lookup.insert(std::make_pair(2.0, value1)); lookup.insert(std::make_pair(5.0, value2)); lookup.insert(std::make_pair(10.0, value3)); MyMap::iterator p = lookup.upper_bound(1.23); if (p == lookup.begin() || p == lookup.end())     ...; // out of bounds assert(p->second == value1);