in reply to Fold a list using map splices
I've used the splice solution, but it offended me that you have to copy the array just to destroy it. I came up with a version of my mapn function that avoids the splice (and therefore the need to copy as well), by using slices and a pointer.
There are two versions of the function mapn and mapnz. With the former, number of values produced in the last row is just how ever many are left over.
With the latter, it pads (with nulls, hence the 'z') the last list of returned values to be the same size as the rest of the rows. This can be useful for things like tables, where although most browsers will tolorate there being less <td></td> pairs in the last row, they do not render this very well. By using mapnz in conjunction with an 8-char patch I made to CGI.pm so that empty TD's have a inserted, forces most browsers to render the borders around missing values.
#! perl -slw use strict; use CGI qw[td Tr :table caption]; sub mapn (&@) { my($c, $n, $s) = (shift, shift, 0); map{ $s+=$n; $c->( @_[($s-$n) .. ($s < @_ ? $s-1 : @_-1) ] ); } 0 .. (@_/$n); } sub mapnz (&@) { my($c, $n, $s) = (shift, shift, 0); map{ $s+=$n; $c->( @_[($s-$n) .. ($s - 1) ] ); } 0 .. (@_/$n); } my @tabular_data = map{ 1000+int rand 8999 } 1 .. 31; print table( {border=>1}, $/, mapn{ Tr( td( \@_ ) ).$/; } 5, @tabular_data ); print table( {border=>1}, $/, caption('Columns: ' . $_), $/, mapnz{ Tr( td( \@_ ) ).$/ } $_, @tabular_data ) for 3 .. 8; __END__ C:\test>236799 <table border="1"> <tr><td>4978</td> <td>7782</td> <td>3230</td> <td>3524</td> <td>7570< +/td></tr> <tr><td>9627</td> <td>4424</td> <td>7968</td> <td>2523</td> <td>1838< +/td></tr> <tr><td>9843</td> <td>8797</td> <td>5034</td> <td>8499</td> <td>3683< +/td></tr> <tr><td>5591</td> <td>2402</td> <td>6131</td> <td>2649</td> <td>5917< +/td></tr> <tr><td>1333</td> <td>7874</td> <td>7031</td> <td>2269</td> <td>3766< +/td></tr> <tr><td>2151</td> <td>1350</td> <td>7235</td> <td>5986</td> <td>1447< +/td></tr> <tr><td>2627</td></tr> </table> <table border="1"> <caption>Columns: 3</caption> <tr><td>4978</td> <td>7782</td> <td>3230</td></tr> <tr><td>3524</td> <td>7570</td> <td>9627</td></tr> <tr><td>4424</td> <td>7968</td> <td>2523</td></tr> <tr><td>1838</td> <td>9843</td> <td>8797</td></tr> <tr><td>5034</td> <td>8499</td> <td>3683</td></tr> <tr><td>5591</td> <td>2402</td> <td>6131</td></tr> <tr><td>2649</td> <td>5917</td> <td>1333</td></tr> <tr><td>7874</td> <td>7031</td> <td>2269</td></tr> <tr><td>3766</td> <td>2151</td> <td>1350</td></tr> <tr><td>7235</td> <td>5986</td> <td>1447</td></tr> <tr><td>2627</td> <td> </td> <td> </td></tr> </table>
2) The only way of discovering the limits of the possible is to venture a little way past them into the impossible
3) Any sufficiently advanced technology is indistinguishable from magic.
Arthur C. Clerk.
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Re^2: Fold a list using map splices
by Aristotle (Chancellor) on Feb 22, 2003 at 00:03 UTC | |
by BrowserUk (Patriarch) on Feb 22, 2003 at 06:31 UTC | |
by Aristotle (Chancellor) on Feb 22, 2003 at 15:24 UTC | |
by hypochrismutreefuzz (Scribe) on Sep 04, 2004 at 01:38 UTC | |
by Aristotle (Chancellor) on Sep 04, 2004 at 03:01 UTC | |
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by BrowserUk (Patriarch) on Feb 22, 2003 at 21:09 UTC |