Split a vector into n sub vectors (rebound)

Question

I am trying to split a vector into n parts. I checked the following solution How to split a vector into n "almost equal" parts

I came out with the following code based on this comment : To get a base number for the size of each part, simply divide the total by the number of parts: 11/3 = 3. Obviously some of the parts will need to be bigger than that to get the proper total, but that's just the remainder: 11 % 3 = 2. So now you know that 2 of the parts will be size 3+1, and whatever's left over will be 3. (Mark Ransom)

int main()
{
std::vector<int> lines;
        int size = 200;
        for(int i = 0; i < size;i++)
        {
            lines.push_back(i);
        }
        int p = 6;
        int right = round((double)size/(double)p);
        for(int i = 0; i < p;i++)
        {
            if( i < size - left)
            {
                vector<int> v;
                for(int j = 0; j < right; j++)
                {
                    v.push_back(lines[j]);
                }
                cout << v.size() << endl;

            }
            else if (i > size - left)
            {
                vector<int> v;
                for(int k = 0; k < right; k++)
                {
                    v.push_back(lines[k]);
                }
                cout << v.size() << endl;
            }
        }
   return 0;
}

Output with p = 6 and size = 200 is : 33,33,33,33,33,33 = 198

Output with p = 6 and size = 1000 is : 167,167,167,167,167,167 = 1002

both outputs are wrong. What am i missing?

After editing:

So Let me understand. We increment i by right which represents the size of a chunk or sub-vector. While i is less than the size-right we do nothing. When i becomes greater we have to deal with the Leftovers we change the size of the chunk by right = size - i.

int main()
{
    std::vector<int> lines;
            int size = 1000;
            for(int i = 0; i < size;i++)
            {
                lines.push_back(i);
            }
            int p = 6;
            int right = round((double)size/(double)p);
            int left = size % p;
            for(int i = 0; i < size; i+= right)
            {
                if(i < size - right)
                {
                    vector<int> v;
                    //MAJOR CORRECTION
                    for(int j = i; j < (i+right); j++)
                    {
                        v.push_back(lines[j]);
                    }
                    cout << v.size() << endl;
    
                }
                else
                {
                    right = size - i;
                    vector<int> v;
                    //Major Correction
                    for(int k =i; k < size; k++)
                    {
                        v.push_back(lines[k]);
                    }
                    cout << v.size() << endl;
    
                }

return 0;
}

Thank you.

output: 33 33 33 33 33 33 2 = 200

For one thing, you are using `i` in the outer loop and then in the inner loop you are again calling your variable `i`. It's not quite clear which one is used now, so you may want to call that differently. — CompuChip, Nov 06 '13 at 22:15
I also don't quite get the size - left `if`-statement. Your `right` is the "standard" size of the chunks, right? So you can just keep on taking `right` elements off the vector, until you notice that `i < size - right`, then you just set `right = size - i` and you're done. — CompuChip, Nov 06 '13 at 22:17
But you are starting each vector at the next value of `i`, right? Don't you want something like `i += right` in your outer loop? — CompuChip, Nov 06 '13 at 22:30
Shouldn't the `right = size - i;` be in your `else` instead of your `if`? :-) — CompuChip, Nov 06 '13 at 22:37

hasan · Answer 1 · 2013-11-06T22:26:26.550

int right = size/p; // don't round! this floors.
int left = size % p; // this one is correct.
for(int i = 0; i < p;i++)
        {
            if( i < size - left)
            {
                vector<int> v;
                for(int j = 0; j < right; j++) // counters, you used i here.
                {
                    v.push_back(lines[j]); // and here.
                }
                cout << v.size() << endl;

            }
            else if (i >= size - left)// sorry equal is here. try >= not > , comment with results.
            {
                vector<int> v;
                for(int j = 0; j < right+1; j++) // and here
                {
                    v.push_back(lines[j]); // and here
                }
                cout << v.size() << endl;
            }
        }

you edited right. question before had (i) as counter for all loops. right?? — hasan, Nov 06 '13 at 22:30

score 0 · Answer 2 · answered Jun 23 '17 at 11:12

Think your idea in other way:
p (parts) = 3, size = 11, ceil(11/3) = 4 so 4+4+3 = 11

same for other p = 6, size = 200 ceil(200/6) = 34 so, 34+34+34+34+34+30 = 200

int p = 6;
size_t nLimit = ceil((double)lines.size()/p);
// if you don't want to contain the leftover element within p elements, use floor
vector<int>::iterator start = lines.begin();
for(size_t i = 0; i < lines.size(); i+=nLimit){
    // Just use the constructor/insert function
    vector<int> v(start+i, start+std::min<size_t>(i+nLimit, lines.size()));
    cout<<v.size()<<endl;

}

Working code here: http://ideone.com/6V7rSX

Split a vector into n sub vectors (rebound)

Thank you.

2 Answers2