CODEWITHSUNDEEP
c++arraysloops
bob blob
bob blob

Reputation: 2341

c++ checking an array for a specific range of values?

i would like to check an array for a specific range of values. ie, the range of values is from 0 --> 9 and the actual array is 50 elements large.

i also want to keep track of how many of each value there is. ie, if there are 3 zeroes, 8 ones and 5 two's, then my final vector should look like, 3 8 5.

i was able to solve it with the code below BUT, i realized that my range values needs to be equal to my array size, otherwise it does not check all elements.

is there a better way to do this?

int main() {

int intensityRange = 10;
int cloudSize = 10;

int cloud [] = {0, 3, 3, 2, 1, 5, 2, 3, 5, 2};
vector <int> totalGreyValues;
int k = 0;

for (int i = 0; i < intensityRange; i++) {
   for (int j = 0; j < cloudSize; j++) {
      if (cloud[j] == i) {
         k = k + 1;
         cout << "   " << k;
      }
      else
        cout << "  no match  ";
   }
   totalGreyValues.push_back (k);
   k = 0;
}

cout << endl << endl << totalGreyValues.size();

for (int h = 0; h < totalGreyValues.size(); h ++)
   cout << "   " << totalGreyValues[h];

// values --> 0 1 2 3 4 5 6 7 8 9
// answer --> 1 1 3 3 0 2 0 0 0 0 

return 0;
}

Upvotes: 3

Views: 6102

Answers (4)

Sebastian Mach
Sebastian Mach

Reputation: 39089

If you have large enough empty regions, you can try a multiset, together with some of C++' new facilities:

#include <set>
#include <iostream>

int main () {
    int vals[] = { 0, 1, 2, 3, 4, 5, 5, 5, 6 };

    std::multiset <int> hist;
    for (auto const &v : vals)
        if (v >= 3 && v <= 5) hist.insert (v);

    for (auto const &v : hist)
        std::cout << v << " -> " << hist.count (v) << '\n';
}

If your data is densely populated, a std::vector might give superiour results:

#include <algorithm>
#include <iostream>

int main () {
    using std::begin; using std::end;

    int vals[] = { 1, 2, 4, 5, 5, 5, 6 };

    const auto val_mm  = std::minmax_element (begin(vals), end(vals));
    const int  val_min = *val_mm.first,
               val_max = *val_mm.second + 1;

    std::vector<int> hist (val_max - val_min);

    for (auto v : vals)
        ++hist [v - val_min];

    for (auto v : vals)
        std::cout << v << " -> " << hist[v-val_min] << '\n';
}

Upvotes: 0

Open AI - Opting Out
Open AI - Opting Out

Reputation: 24133

Use a std::map and the std::accumulate function:

#include <map>
#include <algorithm>

typedef std::map<int, int> Histogram;

Histogram& addIfInRange(Histogram& histogram, const int value)
{
    if(inRange(value))
    {
        ++histogram[value];
    }
    // else don't add it

    return histogram;
}

Histogram histogram =
    std::accumulate(data, data + size, Histogram(), addIfInRange);

Upvotes: 0

pmr
pmr

Reputation: 59811

If your range is continuous I would prefer a boost::vector_property_map.

#include <boost/property_map/vector_property_map.hpp>
#include <iostream>

int main()
{
  boost::vector_property_map<unsigned int> m(10); // size of expected range

  std::vector<int> cloud = {0, 3, 3, 2, 1, 5, 2, 3, 5, 2};
  for(auto x : cloud) { m[x]++; }
  for(auto it = m.storage_begin(); it != m.storage_end(); ++it) { 
    std::cout << *it << " ";
  }
  std::cout << std::endl;

  return 0;
}

If your range does not start at 0 you can use IndexMap template argument to remap the indices. This will also work if you map a non continous set of values that you want to count into a continous range. You might need to perform a check if you only want to count specific values, but given the expensiveness of the count operation, I'd rather count them all instead of checking what to count.

Upvotes: 0

Pillum
Pillum

Reputation: 132

It's much easier to use std::map:

int size = 50;
int data[size] = { 1, 2, 3, 4, 5, ... };

std::map<int, int> mymap;

for(int i = 0; i < size; i++)
{
   if(data[i] >= min && data[i] <= max)
      mymap[data[i]] = mymap[data[i]] + 1;
}

This saves some space, because you don't save unused values and the loop count is also much smaller, because you only process once per value.

Upvotes: 4

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