CODEWITHSUNDEEP
c++stlset
Vijay
Vijay

Reputation: 67221

count of elements in a set (not total count)

I have a set of strings in c++.

i am inserting into that set as :

m.insert("1-2-35-2");
m.insert("1-2-36-1");
m.insert("1-2-37-2");
m.insert("1-2-38-1");
m.insert("1-2-39-2");
m.insert("2-2-40-1");
m.insert("2-2-41-2");
m.insert("2-2-42-1");
m.insert("1-2-43-2");
m.insert("1-2-44-1");
m.insert("1-2-45-2");
m.insert("1-2-46-1");
m.insert("1-2-47-2");

i want to calculate the count of all the strings inside the set which start with "2-"(count =3) and also which start with "1-"(count=10).

is there any way to do it. I tried with lower_bound and upper_bound but its giving me some errors.

errors are coming for the statement:

int i=it_upper-it_lower;

I am using solaris SPARC OS.

i just tested this program 

#include <iostream>
#include <iterator>
#include <list>
using namespace std;

int main () {
  list<int> mylist;
  for (int i=0; i<10; i++) mylist.push_back (i*10);

  list<int>::iterator first = mylist.begin();
  list<int>::iterator last = mylist.end();

  cout << "The distance is: " << distance(first,last) << endl;

  return 0;
}

it gives me compilation error:

line 13: Error: Could not find a match for std::distance<std::ForwardIterator, std::Distance>(std::list<int, std::allocator<int>>::iterator, std::list<int, std::allocator<int>>::iterator).
1 Error(s) detected.

Upvotes: 0

Views: 637

Answers (2)

Some programmer dude
Some programmer dude

Reputation: 409176

If you have a modern compiler that supports lambdas, you could use those as the predicate to count_if:

auto if_s_1 = [](const std::string &s) { return s.find("1-") == 0; }
auto if_s_2 = [](const std::string &s) { return s.find("2-") == 0; }

int count1 = std::count_if(m.begin(), m.end(), if_s_1);
int count2 = std::count_if(m.begin(), m.end(), if_s_2);

Upvotes: 0

2r2w
2r2w

Reputation: 1509

Sorry. Wrong answer
Update: count_if is an algorithm to count elements based on function. Try like in this example:

bool struct key_part: public std::unary_function< std::string, bool >
{
    std::string _part;
    key_part(const std::string part):_part(part){}
    bool operator()(std::string &s)
    {
      return s.find(_part)!=std::string::npos;
    }
}
std::count_if( m.begin(), m.end(), key_part("1-") );

It will count all elements that contains "1-" as part of key

Upvotes: 2

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