filling a boost vector or matrix
Solution 1
Because the vector models a standard random access container you should be able to use the standard STL algorithms. Something like:
c_vector<float,N> vec;
std::fill_n(vec.begin(),N,0.0f);
or
std::fill(vec.begin(),vec.end(),0.0f);
It probably also is compatible with Boost.Assign but you'd have to check.
Solution 2
I have started using boost::assign
for cases that I want to statically assign specific values (examples lifted from link above).
#include <boost/assign/std/vector.hpp>
using namespace boost::assign; // bring 'operator+()' into scope
{
vector<int> values;
values += 1,2,3,4,5,6,7,8,9;
}
You can also use boost::assign
for maps.
#include <boost/assign/list_inserter.hpp>
#include <string>
using boost::assign;
std::map<std::string, int> months;
insert( months )
( "january", 31 )( "february", 28 )
( "march", 31 )( "april", 30 )
( "may", 31 )( "june", 30 )
( "july", 31 )( "august", 31 )
( "september", 30 )( "october", 31 )
( "november", 30 )( "december", 31 );
You can allow do direct assignment with list_of()
and map_list_of()
#include <boost/assign/list_of.hpp> // for 'list_of()'
#include <list>
#include <stack>
#include <string>
#include <map>
using namespace std;
using namespace boost::assign; // bring 'list_of()' into scope
{
const list<int> primes = list_of(2)(3)(5)(7)(11);
const stack<string> names = list_of( "Mr. Foo" )( "Mr. Bar")
( "Mrs. FooBar" ).to_adapter();
map<int,int> next = map_list_of(1,2)(2,3)(3,4)(4,5)(5,6);
// or we can use 'list_of()' by specifying what type
// the list consists of
next = list_of< pair<int,int> >(6,7)(7,8)(8,9);
}
There are also functions for repeat()
, repeat_fun()
, and range()
which allows you to add repeating values or ranges of values.
Solution 3
The recommended way looks like this:
boost::numeric::ublas::c_vector<float, N> v;
v = boost::numeric::ublas::zero_vector<float>(N);
v = boost::numeric::ublas::scalar_vector<float>(N, value);
The same is for matrix types:
boost::numeric::ublas::matrix<float> m(4,4);
m = boost::numeric::ublas::identity_matrix<float>(4,4);
m = boost::numeric::ublas::scalar_matrix<float>(4,4);
m = boost::numeric::ublas::zero_matrix<float>(4,4);
Solution 4
Have you tried this?
ublas::c_vector v = ublas::scalar_vector(N, myScalar);
Mr Fooz
Updated on June 12, 2022Comments
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Mr Fooz almost 2 years
Is there a single-expression way to assign a scalar to all elements of a boost matrix or vector? I'm trying to find a more compact way of representing:
boost::numeric::ublas::c_vector<float, N> v; for (size_t i=0; i<N; i++) { v[i] = myScalar; }
The following do not work:
boost::numeric::ublas::c_vector<float, N> v(myScalar, myScalar, ...and so on..., myScalar); boost::numeric::ublas::c_vector<float, N> v; v = myScalar;
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Mr Fooz almost 15 yearsThat'll work, though it is a full statement as opposed to an expression.
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Mikko Rantanen almost 15 yearsTrue, but it is more compact way which is what you wanted to find based on the post.
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Ankit Roy almost 15 years-1 sorry. You must use "v[i++]" -- "v[++i]" will skip initialisation of v[0] and overwrite the memory past the end of the vector.
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Mr Fooz almost 15 yearsThe STL algorithms do seem to work. Thanks. Boost.Assign doesn't seem to work for me, but I think it's because I'm using a c_vector (const-sized vector) instead of a vector (dynamically sized vector), so push_back doesn't work.
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Mikko Rantanen almost 15 yearsAck. Sorry! I did acknowledge that I had to use the correct unary operator but for some reason I kept thinking ++i is the one that increments i after evaluating. Mostly since everyone prefer i++ and the "i += 1" behaviour seems more logical. Fixed now in any case.. And I guess I should thank you as well, I like 600 rep more than 601!
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Daniel Newby almost 14 yearsThe first example seems to be for std::vector (for which it works), not boost::numeric::ublas::vector (for which it does not work).
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Luis Vito over 12 yearsHow do I get out the value type if I don't know it?
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quant almost 10 yearsThis doesn't answer how you would fill a
boost::numeric::ublas::matrix