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Asked: 2026-06-09T06:16:35+00:00

I need some help with the map function in Perl, it seems to croupte

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I need some help with the map function in Perl, it seems to croupte my arrays.

#!/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 <=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";
}

Now the out put of this gives 

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

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?

Cheers

UPDATE

To confirm I am trying to get the map statment to do the following 

for ($x = 0; $x <=2000; $x++)
{

$degre[$x] = $degre[$x] + $step[$i]
}

altering the code to 

for ($i = 0; $i <=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 <=2000; $x++)

{
$Degre[$x] = $Degre[$x] + $step[$x];
}

gives the following out put 

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

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.

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1 Answer

  1. Editorial Team

    Your @Degre gets changed inside the loop every time where as aa bb and step remains unchanged. 

      print "$aa[1]  $bb[1]  $Degre[1] $step[1] \n";

    The above shows correct value as calculated in 

     @Degre = map {$Degre[$_] + $step[$_]} (1..2000);

    Print @xx and @yy in your print statement instead of @aa and @bb and see the values change as per calculation.

    Put a @Degre=sort(@Degre); just before the for loop and see the results. Below are the results after sorting- 

    1726.50146484375  681.5185546875  0.624771118164063 0.456436157226563 
1726.50146484375  681.5185546875  1.15629577636719 0.456436157226563 
1726.50146484375  681.5185546875  1.7493896484375 0.456436157226563 
1726.50146484375  681.5185546875  2.49296569824219 0.456436157226563 
1726.50146484375  681.5185546875  2.861083984375 0.456436157226563 
1726.50146484375  681.5185546875  3.20767211914063 0.456436157226563 
1726.50146484375  681.5185546875  3.44265747070313 0.456436157226563 
1726.50146484375  681.5185546875  11.8232574462891 0.456436157226563 
1726.50146484375  681.5185546875  12.2711944580078 0.456436157226563 
1726.50146484375  681.5185546875  12.3104858398438 0.456436157226563 
1726.50146484375  681.5185546875  13.2642059326172 0.456436157226563 
1726.50146484375  681.5185546875  13.4784698486328 0.456436157226563 
1726.50146484375  681.5185546875  103.224014282227 0.456436157226563 
1726.50146484375  681.5185546875  103.868133544922 0.456436157226563 
1726.50146484375  681.5185546875  104.103759765625 0.456436157226563 
1726.50146484375  681.5185546875  104.71240234375 0.456436157226563

    As you can see, the calculation is correct i.e. in the first row 0.624771118164063 + 0.456436157226563 is 1.15629577636719 data in the second row and so on.

    However, there is a jump from 3.44265747070313 to 11.8232574462891 at some point. I am not sure why that may be happening happening, but my assumption is that the indexing goes wrong at a certain point. This is resolved using code below

    @Degre = map {$Degre[$_] + $step[$_]} (0..@step-1);

    This time the output is much more consistent in the third column-

    1139.18230471501  192.716943394942  183.715442551381 0.45937396317494 
1139.18230471501  192.716943394942  184.174816514556 0.45937396317494 
1139.18230471501  192.716943394942  184.634190477731 0.45937396317494 
1139.18230471501  192.716943394942  185.093564440906 0.45937396317494 
1139.18230471501  192.716943394942  185.552938404081 0.45937396317494 
1139.18230471501  192.716943394942  186.012312367256 0.45937396317494 
1139.18230471501  192.716943394942  186.471686330431 0.45937396317494 
1139.18230471501  192.716943394942  186.931060293605 0.45937396317494 
1139.18230471501  192.716943394942  187.39043425678 0.45937396317494 
1139.18230471501  192.716943394942  187.849808219955 0.45937396317494 
1139.18230471501  192.716943394942  188.30918218313 0.45937396317494
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