## WeBWorK Problems

### Merging several matrices into one matrix ### Merging several matrices into one matrix

by Paul Pearson -
Number of replies: 3
Hi,

What is the best way to merge several MathObject matrices into one MathObject matrix? In particular, I would like to be able to take several m x 1 matrices (i.e., "column vectors") and merge them into an m x n matrix.

Thanks!

Paul Pearson ### Re: Merging several matrices into one matrix

by Davide Cervone -
If $C1 and $C2 are the ColumnVectors, then
    $M = Matrix($C1,$C2)->transpose;  would do it. But if they are really two-dimensional matrices (like columns from another matrix), then use $M = Matrix($C1->transpose,$C2->transpose)->transpose;

to get the matrix with these columns.

Hope that does it for you.

Davide ### Re: Merging several matrices into one matrix

by Paul Pearson -
Thanks Davide! That did help clarify what ought to be done.

I am using this inside a custom answer checker and noticed that when $C1->transpose was giving results with string representation like [[1,2,3]]. Since the outermost brackets in [[1,2,3]] were undesirable, I removed them using the ->row method:$Row = Matrix($C1->transpose);$Row = $Row->row(1); I put it all together into a little subroutine that takes in an array of column matrices and returns a single matrix comprised of those column matrices. Please let me know if anything in this subroutine needs improvement. ############################ sub put_cols_in_mtx { my @c = @_; my @temp = (); for my$i (0..$#c) { my$Row = Matrix($c[$i])->transpose; $Row =$Row->row(1);
push(@temp,$Row); } return Matrix(@temp)->transpose; } ############################ Thanks! Paul Pearson In reply to Paul Pearson ### Re: Merging several matrices into one matrix by Davide Cervone - It looks good. You could combine the line  my$Row = Matrix($c[$i])->transpose; $Row =$Row->row(1);

into the single command
    my $Row = Matrix($c[$i])->transpose->row(1);  In fact, you could replace  my$Row = Matrix($c[$i])->transpose; $Row =$Row->row(1);
push(@temp,$Row);  with  push(@temp,Matrix($c[$i])->transpose->row(1));  I guess you could also simplify the loop slightly as  for my$c (@c) {
push(@temp,Matrix($c)->transpose->row(1)); }  since you can iterate over your column array. Technically, you could also reuse @c by setting  for my$c (@c) {$c = Matrix($c)->transpose->row(1)}
return Matrix(@c)->transpose;

rather than allocating a second array, but perhaps that is too much.

Other than that, it looks fine.

Davide