?
Solved

2d vector help

Posted on 2006-11-14
5
Medium Priority
?
337 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 400 total points
ID: 17945020
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 400 total points
ID: 17945026
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
ID: 17945030
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
ID: 17945035
Copy is already suggested by DrAske.
0
 
LVL 39

Expert Comment

by:itsmeandnobodyelse
ID: 17946091
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

Never miss a deadline with monday.com

The revolutionary project management tool is here!   Plan visually with a single glance and make sure your projects get done.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Unlike C#, C++ doesn't have native support for sealing classes (so they cannot be sub-classed). At the cost of a virtual base class pointer it is possible to implement a pseudo sealing mechanism The trick is to virtually inherit from a base class…
Article by: evilrix
Looking for a way to avoid searching through large data sets for data that doesn't exist? A Bloom Filter might be what you need. This data structure is a probabilistic filter that allows you to avoid unnecessary searches when you know the data defin…
The viewer will learn how to user default arguments when defining functions. This method of defining functions will be contrasted with the non-default-argument of defining functions.
The viewer will learn how to clear a vector as well as how to detect empty vectors in C++.
Suggested Courses

589 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