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=head1 TITLE
Arrays: transpose()
=head1 VERSION
Maintainer: Jeremy Howard <[EMAIL PROTECTED]>
Date: 22 Sep 2000
Mailing List: [EMAIL PROTECTED]
Number: 272
Version: 1
Status: Developing
=head1 ABSTRACT
It is proposed that a new function C<transpose> be added to Perl.
C<transpose($dim1, $dim2, @list)> would return @list with $dim1 and $dim2
switched. It would return an alias into the original list, not a copy of
the elements.
=head1 DESCRIPTION
It is proposed that Perl implement a function called C<transpose> that
transposes two dimensions of an array, and is evaluated lazily. L<RFC 202>
gives an overview of the proposed multidimensional arrays that
C<transpose> works with. For instance:
@a = ([1,2],[3,4],[5,6]);
@transposed_list = transpose(0,1,@a); # ([1,3,5],[2,4,6])
This is different to C<reshape> (see L<RFC 148>) which does not reorder
its elements:
@a = ([1,2],[3,4],[5,6]);
@reshaped_list = reshape([3,2],@a); # ([1,2,3],[4,5,6])
C<transpose> is its own inverse:
@transposed_list = transpose(0,1,@a); # ([1,3,5],[2,4,6])
@orig_list = transpose(0,1,@transposed_list); # (([1,2],[3,4],[5,6])
@a == @orig_list; # true
If C<transpose> refers to a dimension that does not exist, empty
dimensions autovivify as necessary:
@row_vector = (1,2,3,4);
@col_vector = transpose(0,1,@row_vector); # ([1],[2],[3],[4])
C<transpose> does not make a copy of the elements of its arguments; it
simply create an alias:
@row_vector = (1,2,3,4);
@col_vector = transpose(0,1,@row_vector); # ([1],[2],[3],[4])
$col_vector[[0,1]] = 0;
@row_vector == (1,0,3,4); # True
=head1 IMPLEMENTATION
RFC 90 discusses possible approaches to implementing aliasing.
=head1 REFERENCES
RFC 90: Arrays: merge() and unmerge()
RFC 148: Arrays: Add reshape() for multi-dimensional array reshaping
