Another question about multidimensional vectors

[Markus Pitha]

Hello again,

I have another question about the handling of multidimensiona l vectors.
Actually, it's not difficult when the size is known at the beginning,
but I still wasn't able to create dynamic vectors without knowing the size.
I want to create a vector which contains a vector of ints:

vector<vector<i nt values;

I tried to add the value 35 to the first position of the first vector
and this vector should be on the first position of the "main" vector.
How can I push_back() a vector which contains ints to a vector?
I tried it in a different way like:

vector<intxAxis ;
vector<xAxisyAx is;


But I get compiling errors. I thought about using resize() but both
vectors will be resized in a loop so I have to resize them over and over
again. Moreover I didn't find a conclusion with resize() either. Why do
I actually have to resize them although vectors are dynamic types?
And how can I solve this issue?


Markus

[Jim Langston]

Re: Another question about multidimensiona l vectors

"Markus Pitha" <newsgroupsNOSP AM@pithax.netwr ote in message
news:1403f$4724 60be$54705512$2 1755@news.chell o.at...

Hello again,
>
I have another question about the handling of multidimensiona l vectors.
Actually, it's not difficult when the size is known at the beginning, but
I still wasn't able to create dynamic vectors without knowing the size.
I want to create a vector which contains a vector of ints:
>
vector<vector<i nt values;
>
I tried to add the value 35 to the first position of the first vector and
this vector should be on the first position of the "main" vector.
How can I push_back() a vector which contains ints to a vector?
I tried it in a different way like:
>
vector<intxAxis ;
vector<xAxisyAx is;
>
>
But I get compiling errors. I thought about using resize() but both
vectors will be resized in a loop so I have to resize them over and over
again. Moreover I didn't find a conclusion with resize() either. Why do I
actually have to resize them although vectors are dynamic types?
And how can I solve this issue?

This help any?

#include <vector>

int main()
{
std::vector<std ::vector<int Data;
std::vector<int Row;
Data.push_back( Row );

Data[0].push_back( 11 );
Data[0].push_back( 12 );

if ( Data.size() < 2 )
Data.push_back( Row );
Data[1].push_back( 21 );
Data[1].push_back( 22 );
}

[Juha Nieminen]

Re: Another question about multidimensiona l vectors

Markus Pitha wrote:

How can I push_back() a vector which contains ints to a vector?

Just resize the vector and push back the int into the first vector.
For example:

values.resize(1 ); // now it has 1 int-vector inside it.
values[0].push_back(35); // Pushes 35 into the first vector.

If you want to *literally* push a vector of ints into 'values', you
can literally do that too. For example:

std::vector<int aVector(1, 35); // initialized to have 1 value, 35
values.push_bac k(aVector);

I tried it in a different way like:
>
vector<intxAxis ;
vector<xAxisyAx is;

I don't really understand what is it that you tried to accomplish
with that. If what you want is to create an x*y double-vector, you can
do it like this:

std::vector<std ::vector<int values(xSize, std::vector<int >(ySize));

Now 'values' will be a vector with xSize vectors inside it, and each
one of these will have ySize ints inside them. Then you can simply
access the values like values[2][3].

Why do
I actually have to resize them although vectors are dynamic types?

You have to resize them *because* they are dynamic types, not *although*.

[Markus Pitha]

Re: Another question about multidimensiona l vectors

Hello,

Jim Langston wrote:

#include <vector>
>
int main()
{
std::vector<std ::vector<int Data;
std::vector<int Row;
Data.push_back( Row );
>
Data[0].push_back( 11 );
Data[0].push_back( 12 );
>
if ( Data.size() < 2 )
Data.push_back( Row );
Data[1].push_back( 21 );
Data[1].push_back( 22 );
}

Thanks, that helped me to solve my problem.

Markus

[Markus Pitha]

Re: Another question about multidimensiona l vectors

Hello,

Juha Nieminen wrote:

std::vector<int aVector(1, 35); // initialized to have 1 value, 35
values.push_bac k(aVector);

std::vector<std ::vector<int values(xSize, std::vector<int >(ySize));

But I didn't know the size. The size will be increased in a recursion,
so I had problems with the right syntax. Jim's example already lead my
to my target.

Markus

[Jim Langston]

Re: Another question about multidimensiona l vectors

"Markus Pitha" <newsgroupsNOSP AM@pithax.netwr ote in message
news:286ef$4724 7b77$54705512$9 710@news.chello .at...

Hello,
>
Jim Langston wrote:
>

>#include <vector>
>>
>int main()
>{
> std::vector<std ::vector<int Data;
> std::vector<int Row;
> Data.push_back( Row );
>>
> Data[0].push_back( 11 );
> Data[0].push_back( 12 );
>>
> if ( Data.size() < 2 )
> Data.push_back( Row );
> Data[1].push_back( 21 );
> Data[1].push_back( 22 );
>}

>
Thanks, that helped me to solve my problem.

Incidently, if you don't want to have to create a variable to push back you
could just do:

#include <vector>

int main()
{
std::vector<std ::vector<int Data;
std::vector<int Row;
Data.push_back( std::vector<int >() );

Data[0].push_back( 11 );
Data[0].push_back( 12 );

if ( Data.size() < 2 )
Data.push_back( std::vector<int >() );
Data[1].push_back( 21 );
Data[1].push_back( 22 );
}

[Tadeusz Kopec]

Re: Another question about multidimensiona l vectors

Markus Pitha wrote:
[snip]

I tried it in a different way like:
>
vector<intxAxis ;

Here you are declaring a variable xAxis.

vector<xAxisyAx is;

Here you treat xAxis as a type name.

It should be
typedef vector<intxAxis ;
vector<xAxisyAx is;
to compile, if I correctly guess what you mean.

[BobR]

Re: Another question about multidimensiona l vectors


Juha Nieminen wrote in message...

Markus Pitha wrote:

How can I push_back() a vector which contains ints to a vector?

>
Just resize the vector and push back the int into the first vector.
For example:
>
values.resize(1 ); // now it has 1 int-vector inside it.
values[0].push_back(35); // Pushes 35 into the first vector.
>
If you want to *literally* push a vector of ints into 'values', you
can literally do that too. For example:
>
std::vector<int aVector(1, 35); // initialized to have 1 value, 35
values.push_bac k(aVector);
>

I tried it in a different way like:

vector<intxAxis ;
vector<xAxisyAx is;

>
I don't really understand what is it that you tried to accomplish
with that. If what you want is to create an x*y double-vector, you can
do it like this:
>
std::vector<std ::vector<int values(xSize, std::vector<int >(ySize));

For that, all you need is:

size_t xSize( 20 ), ySize( 30 );
std::vector<std ::vector<int values( xSize, ySize ); // 20x30

--
Bob R
POVrookie