The first thing to check is that the data consumer (which the OP notes is not them) may be able to actually process the upper-triangular matrix as-is; look at LAPACK, which has routines that operate on triangular matrices directly without needing to copy - in other words, this task may not actually be needed.

If it is, the approach I would take using PDL is to pre-allocate a correctly-sized disk-based ndarray (so that RAM is not a limitation) using PDL::IO::FastRaw (untested), from perldl: 

use PDL::IO::FastRaw;
$pdl = mapfraw('fname', {Creat => 1, Dims => [460_000, 460_000], Datat
+ype => double()});

[download]
It looks like currently PDL::IO::Misc (with rcols) and PDL::IO::CSV don't have a facility to read into an existing (possibly disk-based) ndarray. It would still be possible, albeit slow, to read the file line-by-line, probably using Text::CSV_XS, using slice to insert each row into the ndarray.

Once the ndarray exists, to copy one triangle into the other would be super-easy using PDL::LinearAlgebra::Real#tricpy.

In reply to Re^3: upper or lower triangular matrix to full by etj
in thread upper or lower triangular matrix to full by savita

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.