On 12/17/12 11:24, Larry Evans wrote:

On 12/17/12 09:50, gast128 wrote:

...

Dear all,

we use here the multi_array as a 2 dimensional matrix. Often we want to resize the row or column dependent on some GUI event. Code could be:

void Bla::ResizeRows(size_t nRows) { m_matrix.resize(boost::extents[nRows][m_matrix[0].size()]); }

However this uses the 0-index of row count (i.e. 'm_matrix[0].size()') to determine the size of the columns. Will this not crash if you have 0 rows? And if so is there a better alternative?

wkr. The test driver:

http://svn.boost.org/svn/boost/sandbox/variadic_templates/sandbox/array_dyn/...

produces output:

********reshape demo*********** dir_op=0 shape={ 0, 3} my_data.size()=0 ai= } . shape={ 1, 3} ai= { { 0, 0, 0} } . shape={ 5, 3} ai= { { 0, 0, 0} , { 0, 0, 0} , { 0, 0, 0} , { 0, 0, 0} , { 0, 0, 0} } .

Compilation finished at Mon Dec 17 11:11:25

Which suggests it will work when 1st axis (the row axis) has 0 as it's size. Unfortunately, this is not Boost.MultiArray and it's probably a lot slower since the sizes of the dimensions are all runtime values. Also, the printout when the shape includes a 0, as in:

shape={ 0, 3}

does not have balanced curly brackets:

ai= }

I'm not sure how to handle that yet.

Addition of print_array<.>::visit_empty and corresponding change to array_host seems to solve the empty axis print problem: ********reshape demo*********** dir_op=0 shape={ 3, 0} my_data.size()=0 ai= { { } , { } , { } } . shape={ 3, 1} ai= { { 0} , { 1} , { 2} } . shape={ 3, 5} ai= { { 0, 3, 6, 9, 12} , { 1, 4, 7, 10, 13} , { 2, 5, 8, 11, 14} } . shape={ 0, 5} ai= { } . Compilation finished at Mon Dec 17 12:55:44 HTH. -regards, Larry

On 12/17/12 14:14, gast128 wrote:

This gives at least an assert:

BOOST_ASSERT(size_type(idx - index_bases[0]) < extents[0]);

Isn't there a better solution?

Are you referring to multi_array for the array_dyn alternative mentioned in my OP? Or this this reply not intended for me? Could you provide the complete program that has this statement in it? I've grepped files here: http://svn.boost.org/svn/boost/sandbox/variadic_templates/sandbox/array_dyn for extents, and found none; hence, I'm confused :( -regards, Larry

On 18 December 2012 08:24, gast128 wrote:

I am talking about multi_array, see title. Example code:

void f() { typedef boost::multi_array Matrix;

Matrix m1(boost::extents[2][3]); _ASSERT(m1.size() == 2); _ASSERT(m1[0].size() == 3);

m1.resize(boost::extents[0][3]); _ASSERT(m1.size() == 0); //_ASSERT(m1[0].size() == 3); //<--assert }

Hi, The shape function has the list of multi_array dimensions. This should do it: #include #include <cassert> int main() { typedef boost::multi_array Matrix; Matrix m1(boost::extents[2][3]); assert(m1.shape()[0] == 2); assert(m1.shape()[1] == 3); m1.resize(boost::extents[0][3]); assert(m1.shape()[0] == 0); assert(m1.shape()[1] == 3); return 0; } Cheers, Vitaly

Yes with the shape function it works. Thx. For Larry: with 'alternative' I meant 'alternative ways within the Boost.MultiArray library' (e.g. with the 'shape() function). Still thx for your effort you put in answering my question.