Solved

2d vector help

Posted on 2006-11-14
5
312 Views
Last Modified: 2008-02-01
I'm hoping someone could help me with 2-d vectors.

Could someone tell me how to:

1.  perform a push_back on a 2d vector
2.  perform a resize on a 2d vector
3.  make a copy of a 2d vector

Thanks!
0
Comment
Question by:cfans
  • 3
5 Comments
 
LVL 12

Assisted Solution

by:rajeev_devin
rajeev_devin earned 100 total points
Comment Utility
For 1.

vector<vector<int> > matrix;

vector<int> v;
v.push_back(10);
v.push_back(20);
v.push_back(30);

matrix.push_back(v);
0
 
LVL 9

Accepted Solution

by:
DrAske earned 100 total points
Comment Utility
1)
vector< vector<int> > matrix(max_index); // to set the size of the array

for(int i = 0; i<matrix.size(); ++i)
    matrix[i].reserve(max_index);  // to set the size of each column .. Now the matrix is (max_index X max_index)

// set all indecies to 0
for(int x = 0 ;x<matrix.size(); ++x)
    for(int y = 0 ; y<matrix[0].size(); ++y)
           matrix[i][j] = 0;

OR:

vector<int> v(max_index);
vector< vector<int> vv(max_index);
for(int i = 0; i<v.size(); ++i)
    v.push_back(0);

vv.push_back(v);


2)

matrix.resize(max_index+1, vector<int>(max_index)); // max_index+1 is the new size of the matrix

3)
I didn't do that before, but try this

vector< vector<int> > copyMatrix = matrix;

regards,Ahmad;


0
 
LVL 12

Expert Comment

by:rajeev_devin
Comment Utility
2.
//for 10x20
vector<vector<int> > matrix;

matrix.resize(10);
for (int i = 0; i < 10; ++i)
   matrix[i].resize(20);

0
 
LVL 12

Expert Comment

by:rajeev_devin
Comment Utility
Copy is already suggested by DrAske.
0
 
LVL 39

Expert Comment

by:itsmeandnobodyelse
Comment Utility
You can set both dimensions when creating the 2d array, e. g.

    vector<vector<int> > matrix(10, vector<int>(20, 0) );  // 10 x 20 all zeros

>>>> 1.  perform a push_back on a 2d vector

push_back is an operation defined for a 1d array. So if you look at the first index as the ROW index, you would add a new row by push_back.

For a 2d array push_back isn't well defined cause normally a 2d array has the same column size for all rows. A push_back for a row would add one cell to that row, what might be strange. If you want to increase the number of columns for all rows you better use the resize function for any row:

 vector<vector<int> >::iterator i;
 for (i = matrix.begin(); i != matrix.end(); ++i)
       i->resize(i->size()+1, 0);  // increment and set to 0


Regards, Alex

0

Featured Post

Top 6 Sources for Identifying Threat Actor TTPs

Understanding your enemy is essential. These six sources will help you identify the most popular threat actor tactics, techniques, and procedures (TTPs).

Join & Write a Comment

Article by: SunnyDark
This article's goal is to present you with an easy to use XML wrapper for C++ and also present some interesting techniques that you might use with MS C++. The reason I built this class is to ease the pain of using XML files with C++, since there is…
In days of old, returning something by value from a function in C++ was necessarily avoided because it would, invariably, involve one or even two copies of the object being created and potentially costly calls to a copy-constructor and destructor. A…
The goal of the tutorial is to teach the user how to use functions in C++. The video will cover how to define functions, how to call functions and how to create functions prototypes. Microsoft Visual C++ 2010 Express will be used as a text editor an…
The viewer will learn additional member functions of the vector class. Specifically, the capacity and swap member functions will be introduced.

772 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

15 Experts available now in Live!

Get 1:1 Help Now