Databases
StackOverflow2013
Postsdbo
POperformance difference between while (each) and foreach in Perl
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POperformance difference between while (each) and foreach in Perl
    primarykey
    data
    text
    <p>The hash that I tested contains around 70000 colleges and each college contains around 20 students. I tried it 5 times and following are the results. There is considerable difference in foreach performance and while (each) performance. Why is that so?</p> <p>Code with while loop:</p> <pre><code>while ( my ($college_code, $college_info_hr) = each (%{$college_data_hr}) ) { while ( my ($student_num, $student_info_hr) = each (%{$college_info_hr-&gt;{'students'}}) ) { if($student_num &lt; 104000) { ## Delete the info of students before 2004. delete $college_info_hr-&gt;{'students'}{$student_num}; } } } </code></pre> <p>Code with foreach loop:</p> <pre><code>foreach my $college_code (keys %{$college_data_hr}) { foreach my $student_num (keys %{$college_data_hr-&gt;{$college_code}{'students'}}) { if($student_num &lt; 104000) { ## Delete the info of students before 2004. delete $college_data_hr-&gt;{$college_code}{'students'}{$student_num}; } } } </code></pre> <p><strong>When the the number of colleges are 70,000 then the execution times are:</strong></p> <p>For the code with while loop (Interval time is in seconds):</p> <p>Interval time: 2.186621</p> <p>Interval time: 2.058644</p> <p>Interval time: 2.055645</p> <p>Interval time: 2.101637</p> <p>Interval time: 2.124632</p> <p>For the code with foreach loop: (Interval time is in seconds)</p> <p>Interval time: 1.341768</p> <p>Interval time: 1.436751</p> <p>Interval time: 1.346529</p> <p>Interval time: 1.302775</p> <p>Interval time: 1.356765</p> <p><strong>When the the number of colleges are 248,000 then the execution times are:</strong></p> <p>(execution times for while loop)</p> <p>Interval time: 9.084427</p> <p>Interval time: 8.438684</p> <p>Interval time: 9.329338</p> <p>Interval time: 9.169687</p> <p>(execution times for foreach loop)</p> <p>Interval time: 5.502048</p> <p>Interval time: 6.386692</p> <p>Interval time: 5.596032</p> <p>Interval time: 5.620144</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USvinod
    1. USvinod
    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. VO
      singulars
      1. POperformance difference between while (each) and foreach in Perl
      1. This table or related slice is empty.
      1. VTUpMod
    1. CO`each keys ...` ?
      singulars
      1. POperformance difference between while (each) and foreach in Perl
      1. USmob
    2. COMore important than the execution time is how it changes wrt the input size. Time the same code with double and triple input sizes and look at the growth.
      singulars
      1. POperformance difference between while (each) and foreach in Perl
      1. USperreal
    3. CO@mob, sorry. That was a mistake. Edited it.
      singulars
      1. POperformance difference between while (each) and foreach in Perl
      1. USvinod
 

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