Databases
StackOverflow2013
Postsdbo
POPerl Map Function not working as expected
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POPerl Map Function not working as expected
    primarykey
    data
    text
    <p>I need some help with the map function in Perl, it seems to croupte my arrays.</p> <pre><code>#!/usr/bin/perl use Math::Trig; my @Degre = map {rand(360)} (1..2000); my @step= map {rand(.5)} (1..2000); my @aa = map {rand(2000)} (1..2000); my @bb = map {rand(2000)} (1..2000); for ($i = 0; $i &lt;=100; $i++) { my @xx = map {$aa[$_]*(cos($Degre[$_])*(pi/180))}(1..2000); my @yy = map {$bb[$_]*(cos($Degre[$_])*(pi/180))}(1..2000); @Degre = map {@Degre[$_] + @step[$_]} (1..2000); print "@bb[1] @aa[1] @Degre[1] @step[1] \n"; } </code></pre> <p>Now the out put of this gives </p> <pre><code>1146.56471948439 1909.33326800968 329.443529905881 0.117635819122725 1146.56471948439 1909.33326800968 343.482356802257 0.117635819122725 1146.56471948439 1909.33326800968 164.500200570578 0.117635819122725 1146.56471948439 1909.33326800968 252.734665366625 0.117635819122725 1146.56471948439 1909.33326800968 274.983382178209 0.117635819122725 1146.56471948439 1909.33326800968 324.609187610893 0.117635819122725 1146.56471948439 1909.33326800968 261.96207333817 0.117635819122725 1146.56471948439 1909.33326800968 279.442105351764 0.117635819122725 </code></pre> <p>With the 3rd column being the degrees, I don't see why it seems to jump around randomly when I expected it to increase in 0.117635..... steps? </p> <p>Cheers</p> <p>UPDATE </p> <p>To confirm I am trying to get the map statment to do the following </p> <pre><code>for ($x = 0; $x &lt;=2000; $x++) { $degre[$x] = $degre[$x] + $step[$i] } </code></pre> <p>altering the code to </p> <pre><code>for ($i = 0; $i &lt;=100; $i++) { my @xx = map {$aa[$_]*(cos($Degre[$_])*(pi/180))}(1..2000); my @yy = map {$bb[$_]*(cos($Degre[$_])*(pi/180))}(1..2000); #@Degre = map {$Degre[$_] + $step[$_]} (1..2000); for ($x = 0; $x &lt;=2000; $x++) { $Degre[$x] = $Degre[$x] + $step[$x]; } </code></pre> <p>gives the following out put </p> <pre><code>738.346205775827 646.171091419262 395.07480695473 0.484472140779317 738.346205775827 646.171091419262 395.559279095509 0.484472140779317 738.346205775827 646.171091419262 396.043751236288 0.484472140779317 738.346205775827 646.171091419262 396.528223377068 0.484472140779317 738.346205775827 646.171091419262 397.012695517847 0.484472140779317 738.346205775827 646.171091419262 397.497167658626 0.484472140779317 738.346205775827 646.171091419262 397.981639799406 0.484472140779317 738.346205775827 646.171091419262 398.466111940185 0.484472140779317 </code></pre> <p>as you can see the degree column now incremented correctly by the step value each time thought the loop. So why does map not do the same.</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USDevilWAH
    1. USDevilWAH
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. COone question does the line "@Degre = map {$Degre[$_] + $step[$_]} (1..2000);" over right the original array values? or add to the array?
      singulars
      1. POPerl Map Function not working as expected
      1. USDevilWAH
    2. COIncidentally, `map {} (1..2000)` is an inefficient way of doing things, because it creates a 2000-element array populated with the numbers 1 to 2000. A for loop that does the same thing would be more efficient: `$Degre[$_] += $step[$_] for (1..2000)`
      singulars
      1. POPerl Map Function not working as expected
      1. USdan1111
    3. COWhen i tested a for loop (using the code in my question above). and bench marked it against using "map" it was signifently slower. I will try again with the code you suggest. Cheers :)
      singulars
      1. POPerl Map Function not working as expected
      1. USDevilWAH
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload