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Sorting Problem HELp

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Join Date: Jul 2009

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Reputation: zsady is an unknown quantity at this point

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zsady

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Sorting Problem HELp

Aug 4th, 2009

Hi I have a vector which contains a number of objects. Inside these objects are 2 attributes. the X and the Y coordinates. How Can I sort them from top to bottom 1st then left to right?

e.g

0,0
1,0
0,5,
3,1
2,5

the output would be
0,0
0,5
1,0
2,5
3,1

since this needs to check not 1 but 2 attributes, im a bit stumped. Any help would be appreciated.

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Join Date: Mar 2008

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Sky Diploma Sky Diploma is offline

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Re: Sorting Problem HELp

Aug 4th, 2009

I guess it is just a question of grouping.

The Basic Approach would be like this:

First you will need to start with sorting the "X" coordinates. After that. Group all the Objects having the same "X" coordinate. After that. In that particular group ... Sort the "Y" coordinates.

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Join Date: Mar 2005

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invisal

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Re: Sorting Problem HELp

Aug 4th, 2009

Sorting concept is simple: from the least to the greatest or from the greatest to the least. To do so, you need to do comparison. So, the magic trick is comparison-rule (which is greater and which is lesser). For example: we got 5 points (consisting of x-axis and y-axis).

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
           X, Y
Point-A   (5, 10)
Point-B   (4, 6)
Point-C   (6, 7)
Point-D   (5, 9)
Point-E   (4, 9)
           X, Y
Point-A   (5, 10)
Point-B   (4, 6)
Point-C   (6, 7)
Point-D   (5, 9)
Point-E   (4, 9)

And then I create my comparison-rule:

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(Toggle Plain Text)

If  Point1.X is greater than Point2.X then  Point1.X is greater than Point2
If  Point1.X is equal to Point2.X then 
   | If Point1.Y is greater than Point2.Y  then Point1 is great than Point2
   | If Point1.Y is lesser than Point2.Y  then Point1 is lesser than Point2
If  Point1.X is lesser than Point2.X then  Point1.X is lesser than Point2

Using this comparison with some comparison-process. I have finally sorted my points.

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Result after sort
           X, Y
Point-C   (6, 7)
Point-A   (5, 10)
Point-D   (5, 9)
Point-E   (4, 9)
Point-B   (4, 6)

Now, time to change my comparison-rule so that I would get difference result:

New comparison-rule:

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If Point1.X + Point1.Y > Point2.X + Point2.Y Then  Point1 is greater than Point2
Else  Point1 is lesser than Point2.

After do comparison-process with this new rule, I got difference result:

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Result after sort
           X, Y
Point-A   (5, 10)  // 5 + 10 = 15
Point-D   (5, 9)   // 5 + 9 = 14
Point-C   (6, 7)    // 6 + 7 = 13
Point-E   (4, 9)   // 4 + 9 = 13
Point-B   (4, 6)   // 4 + 6 = 10

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Join Date: Dec 2008

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firstPerson firstPerson is offline

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Re: Sorting Problem HELp

Aug 4th, 2009

use the std::sort algo. you will need to give it your compare function
which should compare the x first then the y.

example :

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 C++ Syntax (Toggle Plain Text) 
#include<iostream>
#include<vector>
#include<algorithm>
 
using std::vector;
using std::cout;
using std::cin;
using std::endl;
 
 
int main()
{  
 
	vector< vector<float> > vec2d(2,vector<float>(2,0));
 
	for(int i =0; i < vec2d.size(); i++)
	{
		cout<<"Enter "<<vec2d[i].size()<<" numbers for col "<<i<<"\n";
 
		for(int j = 0; j < vec2d[i].size(); j++)
		{
 
			cin >> vec2d[i][j];			
		}
 
	}
 
	std::sort(vec2d.begin(),vec2d.end());
 
	for(int i =0; i < vec2d.size(); i++)
	{
 
		for(int j = 0; j < vec2d[i].size(); j++)
		{
 
			cout<<vec2d[i][j]<<" ";
		}
 
		cout<<"\n";
	}		
}
#include<iostream>
#include<vector>
#include<algorithm>

using std::vector;
using std::cout;
using std::cin;
using std::endl;


int main()
{  

	vector< vector<float> > vec2d(2,vector<float>(2,0));

	for(int i =0; i < vec2d.size(); i++)
	{
		cout<<"Enter "<<vec2d[i].size()<<" numbers for col "<<i<<"\n";

		for(int j = 0; j < vec2d[i].size(); j++)
		{

			cin >> vec2d[i][j];			
		}

	}

	std::sort(vec2d.begin(),vec2d.end());
	
	for(int i =0; i < vec2d.size(); i++)
	{
 
		for(int j = 0; j < vec2d[i].size(); j++)
		{

			cout<<vec2d[i][j]<<" ";
		}
		
		cout<<"\n";
	}		
}