find the lowest number?
i get an array conataining a lot off numbers like this: 567 551 540 540 540 533 531 526 493 476 468 429 421 520 how do i find the lowest or the higest number in this series? //Dave -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
AW: find the lowest number?
@numbers = (44, 55, 38, 10 , 5, 7);
@numbers = sort { $a=$b } @number;
print $numbers[0]; # the lowest
-Ursprüngliche Nachricht-
Von: David Samuelsson (PAC) [mailto:[EMAIL PROTECTED]]
Gesendet am: Freitag, 30. August 2002 10:23
An: '[EMAIL PROTECTED]'
Betreff: find the lowest number?
i get an array conataining a lot off numbers like this:
567
551
540
540
540
533
531
526
493
476
468
429
421
520
how do i find the lowest or the higest number in this series?
//Dave
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AW: find the lowest number?
@numbers[$#numbers]; # highest
@numbers[-1]; # highest
-Ursprüngliche Nachricht-
Von: Angerstein [mailto:[EMAIL PROTECTED]]
Gesendet am: Freitag, 30. August 2002 10:34
An: [EMAIL PROTECTED]
Betreff: AW: find the lowest number?
@numbers = (44, 55, 38, 10 , 5, 7);
@numbers = sort { $a=$b } @number;
print $numbers[0]; # the lowest
-Ursprüngliche Nachricht-
Von: David Samuelsson (PAC) [mailto:[EMAIL PROTECTED]]
Gesendet am: Freitag, 30. August 2002 10:23
An: '[EMAIL PROTECTED]'
Betreff: find the lowest number?
i get an array conataining a lot off numbers like this:
567
551
540
540
540
533
531
526
493
476
468
429
421
520
how do i find the lowest or the higest number in this series?
//Dave
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AW: find the lowest number?
sort will sort like windows does with filename if you do this that way. example sort do: 1, 16, 20, 3, 35, 4, 400 not: 1,3,4,16,20,35,400 -Ursprüngliche Nachricht- Von: Ramprasad A Padmanabhan [mailto:[EMAIL PROTECTED]] Gesendet am: Freitag, 30. August 2002 10:39 An: [EMAIL PROTECTED] Betreff: Re: find the lowest number? David Samuelsson wrote: i get an array conataining a lot off numbers like this: 567 551 540 540 540 533 531 526 493 476 468 429 421 520 how do i find the lowest or the higest number in this series? //Dave @a = qw(121 23 31 4 11); print LOWEST . (reverse sort @a )[0]; -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: find the lowest number?
On Fri, 30 Aug 2002, Ramprasad A Padmanabhan wrote:
@a = qw(121 23 31 4 11);
print LOWEST . (reverse sort @a )[0];
By default sort does a lexical sort, this will not work
Correct way to do this
my @list = qw(121 23 31 4 11);
print LOWEST: , (sort {$a = $b} @list)[0];
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Re: find the lowest number?
on Fri, 30 Aug 2002 08:22:56 GMT, [EMAIL PROTECTED]
(David Samuelsson) wrote:
i get an array conataining a lot off numbers like this:
567
[snipped]
520
how do i find the lowest or the higest number in this series?
There is no need to sort the full array (as others suggested) to just
find the lowest and highest number when an O(n) operation will
suffice:
my ($min, $max);
$min = $max = $array[0];
for (1..@array-1) {
$min = $array[$_] if $array[$_] $min;
$max = $array[$_] if $array[$_] $max;
}
print min = $min, max = $max\n;
--
felix
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Re: find the lowest number?
On 30 Aug 2002, Felix Geerinckx wrote:
There is no need to sort the full array (as others suggested) to just
find the lowest and highest number when an O(n) operation will
suffice:
Precisely the comment that I had a few months back for a similar question.
Read through this thread
http://archive.develooper.com/beginners%40perl.org/msg22716.html
my ($min, $max);
$min = $max = $array[0];
for (1..@array-1) {
$min = $array[$_] if $array[$_] $min;
$max = $array[$_] if $array[$_] $max;
}
print min = $min, max = $max\n;
For further proof here is a benchmarking result
#!/usr/local/bin/perl -w
use strict;
use Benchmark;
my @arr = qw(34 12 23 45 11 91 32);
sub using_sort {
my $min = (sort {$a = $b} @arr)[0];
my $max = (reverse sort {$a = $b} @arr)[0];
}
sub using_for {
my ($min, $max);
$min = $max = $arr[0];
for (1..@arr-1) {
$min = $arr[$_] if $arr[$_] $min;
$max = $arr[$_] if $arr[$_] $max;
}
}
timethese (100, { using_sort = \using_sort,
using_for = \using_for });
=cut
Benchmark: timing 100 iterations of using_for, using_sort...
using_for: 11 wallclock secs (11.60 usr + 0.04 sys = 11.64 CPU) @
85910.65/s (n=100)
using_sort: 8 wallclock secs ( 7.63 usr + 0.06 sys = 7.69 CPU) @
130039.01/s (n=100)
Note that even with two sorts and a reverse the using_sort subroutine
is faster in terms of speed.
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AW: find the lowest number?
fake! you dont need to sort the array to times... because u know where the
lowest hand the higest is.
Less of the half of 11 wallclocks would be what i expect.
-Ursprüngliche Nachricht-
Von: Sudarshan Raghavan [mailto:[EMAIL PROTECTED]]
Gesendet am: Samstag, 31. August 2002 04:11
An: Perl beginners
Betreff: Re: find the lowest number?
On 30 Aug 2002, Felix Geerinckx wrote:
There is no need to sort the full array (as others suggested) to just
find the lowest and highest number when an O(n) operation will
suffice:
Precisely the comment that I had a few months back for a similar question.
Read through this thread
http://archive.develooper.com/beginners%40perl.org/msg22716.html
my ($min, $max);
$min = $max = $array[0];
for (1..@array-1) {
$min = $array[$_] if $array[$_] $min;
$max = $array[$_] if $array[$_] $max;
}
print min = $min, max = $max\n;
For further proof here is a benchmarking result
#!/usr/local/bin/perl -w
use strict;
use Benchmark;
my @arr = qw(34 12 23 45 11 91 32);
sub using_sort {
my $min = (sort {$a = $b} @arr)[0];
my $max = (reverse sort {$a = $b} @arr)[0];
}
sub using_for {
my ($min, $max);
$min = $max = $arr[0];
for (1..@arr-1) {
$min = $arr[$_] if $arr[$_] $min;
$max = $arr[$_] if $arr[$_] $max;
}
}
timethese (100, { using_sort = \using_sort,
using_for = \using_for });
=cut
Benchmark: timing 100 iterations of using_for, using_sort...
using_for: 11 wallclock secs (11.60 usr + 0.04 sys = 11.64 CPU) @
85910.65/s (n=100)
using_sort: 8 wallclock secs ( 7.63 usr + 0.06 sys = 7.69 CPU) @
130039.01/s (n=100)
Note that even with two sorts and a reverse the using_sort subroutine
is faster in terms of speed.
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Re: AW: find the lowest number?
On Fri, 30 Aug 2002, Angerstein wrote: fake! you dont need to sort the array to times... because u know where the lowest hand the higest is. Yes I do know that, you don't have to sort the array two times. Less of the half of 11 wallclocks would be what i expect. I think you should read through the mail properly before crying fake. The 11 seconds is for the subroutine using the foreach loop. Benchmark: timing 100 iterations of using_for, using_sort... using_for: 11 wallclock secs (11.60 usr + 0.04 sys = 11.64 CPU) @ 85910.65/s (n=100) using_sort: 8 wallclock secs ( 7.63 usr + 0.06 sys = 7.69 CPU) @ 130039.01/s (n=100) -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
AW: AW: find the lowest number?
ok, i see. That´s what i thought. -Ursprüngliche Nachricht- Von: Sudarshan Raghavan [mailto:[EMAIL PROTECTED]] Gesendet am: Samstag, 31. August 2002 04:33 An: Perl beginners Betreff: Re: AW: find the lowest number? On Fri, 30 Aug 2002, Angerstein wrote: fake! you dont need to sort the array to times... because u know where the lowest hand the higest is. Yes I do know that, you don't have to sort the array two times. Less of the half of 11 wallclocks would be what i expect. I think you should read through the mail properly before crying fake. The 11 seconds is for the subroutine using the foreach loop. Benchmark: timing 100 iterations of using_for, using_sort... using_for: 11 wallclock secs (11.60 usr + 0.04 sys = 11.64 CPU) @ 85910.65/s (n=100) using_sort: 8 wallclock secs ( 7.63 usr + 0.06 sys = 7.69 CPU) @ 130039.01/s (n=100) -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: AW: find the lowest number?
my $ret_val;
my $i;
if ($#your_array 0){
## do appropriate thing
}
elsif ($#your_array == 0){ ## return the only value it has}
## following is the ELSE part
for (my $i = 0; i $#your_array; ++i)
{
$ret_val = your_array[i+1];
$ret_val = your_array[i] if (your_array[i] your_array[i+1]);
}
## $ret_val contains the max number.
-
Get a bigger mailbox -- choose a size that fits your needs.
Re: find the lowest number?
On Sat, 31 Aug 2002, Sudarshan Raghavan wrote:
For further proof here is a benchmarking result
#!/usr/local/bin/perl -w
use strict;
use Benchmark;
my @arr = qw(34 12 23 45 11 91 32);
sub using_sort {
my $min = (sort {$a = $b} @arr)[0];
my $max = (reverse sort {$a = $b} @arr)[0];
My bad!! this should be
my ($min, $max) = (sort {$a = $b} @arr)[0, -1];
}
sub using_for {
my ($min, $max);
$min = $max = $arr[0];
for (1..@arr-1) {
$min = $arr[$_] if $arr[$_] $min;
$max = $arr[$_] if $arr[$_] $max;
}
}
timethese (100, { using_sort = \using_sort,
using_for = \using_for });
With these changes the benchmarking gets even better
Benchmark: timing 100 iterations of using_for, using_sort...
using_for: 14 wallclock secs (11.89 usr + 0.06 sys = 11.95 CPU) @
83682.01/s (n=100)
using_sort: 4 wallclock secs ( 4.13 usr + 0.02 sys = 4.15 CPU) @
240963.86/s (n=100)
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Re: AW: find the lowest number?
why use sorting and other algos which have non-linear time-complexity. traverse the array once and get the max and min - Get a bigger mailbox -- choose a size that fits your needs.
Re: AW: find the lowest number?
On Fri, 30 Aug 2002, Dharmendra Rai wrote:
The list FAQ requests folks to snip uneccessary lines before replying to
mails. But surely the entire mail cannot be uneccessary. Please leave some
parts of it so that other's in this list know what you are replying to.
my $ret_val;
my $i;
if ($#your_array 0){
## do appropriate thing
}
elsif ($#your_array == 0){ ## return the only value it has}
## following is the ELSE part
for (my $i = 0; i $#your_array; ++i)
{
$ret_val = your_array[i+1];
Do you test your code, this is a syntax error
$your_array[i+1];
$ret_val = your_array[i] if (your_array[i] your_array[i+1]);
Same here. Use the ternary operator for this
$ret_val = ($your_array[i] $your_array[i+1]) ? $your_array[i] : $your_array[i+1];
}
## $ret_val contains the max number.
This is C style coding, Felix had already posted a soln on similar lines.
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Re: find the lowest number?
on Sat, 31 Aug 2002 02:23:20 GMT, [EMAIL PROTECTED] (Sudarshan Raghavan) wrote: On 30 Aug 2002, Felix Geerinckx wrote: There is no need to sort the full array (as others suggested) to just find the lowest and highest number when an O(n) operation will suffice: Precisely the comment that I had a few months back for a similar question. Read through this thread http://archive.develooper.com/beginners%40perl.org/msg22716.html Thanks for this reference (from a time before I discovered the perl beginners list). Benchmark: timing 100 iterations of using_for, using_sort... using_for: 11 wallclock secs (11.60 usr + 0.04 sys = 11.64 CPU) @ 85910.65/s (n=100) using_sort: 8 wallclock secs ( 7.63 usr + 0.06 sys = 7.69 CPU) @ 130039.01/s (n=100) This if for a seven-element array. I did some testing myself for larger array sizes (times are in CPU seconds): Size Loop Sort 1000 0.00 0.01 1 0.02 0.08 10 0.13 1.03 20 0.24 2.18 30 0.37 3.35 So if you have more than 1000 numbers, the loop method will already be faster. In addition, it has the advantage that you don't need all the numbers to be present in memory, since you can calculate min/max while you read the numbers from file. For small array sizes, it doesn't matter which method you use, since the cpu time will be near zero anyway. For larger sizes it does matter, and the loop method is a clear winner. Therefor, imho, your suggestion in March (and mine now :-) to use a loop, is *always* preferable. -- felix -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: find the lowest number?
On 30 Aug 2002, Felix Geerinckx wrote: This if for a seven-element array. I did some testing myself for larger array sizes (times are in CPU seconds): Size Loop Sort 1000 0.00 0.01 1 0.02 0.08 10 0.13 1.03 20 0.24 2.18 30 0.37 3.35 So if you have more than 1000 numbers, the loop method will already be faster. In addition, it has the advantage that you don't need all the numbers to be present in memory, since you can calculate min/max while you read the numbers from file. For small array sizes, it doesn't matter which method you use, since the cpu time will be near zero anyway. For larger sizes it does matter, and the loop method is a clear winner. Therefor, imho, your suggestion in March (and mine now :-) to use a loop, is *always* preferable. I thought on similar lines too when that thread was on, but I convinced myself saying that an unsorted array of 1000 or more elements in your code is a poor design to start with :-) -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: find the lowest number?
on Sat, 31 Aug 2002 03:51:39 GMT, [EMAIL PROTECTED] (Sudarshan Raghavan) wrote: I thought on similar lines too when that thread was on, but I convinced myself saying that an unsorted array of 1000 or more elements in your code is a poor design to start with :-) I beg to differ. From perldoc perldata (my emphasis): Normal arrays are *ordered* lists of scalars indexed by number, starting with 0 and with negative subscripts counting from the end. One of the main features of arrays (compared to hashes) is that you have full control over the order in which the elements are inserted. Many algorithms rely on this order (look e.g. at the GD::Graph module). -- felix -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: find the lowest number?
On 30 Aug 2002, Felix Geerinckx wrote: on Sat, 31 Aug 2002 03:51:39 GMT, [EMAIL PROTECTED] (Sudarshan Raghavan) wrote: I thought on similar lines too when that thread was on, but I convinced myself saying that an unsorted array of 1000 or more elements in your code is a poor design to start with :-) I beg to differ. From perldoc perldata (my emphasis): Normal arrays are *ordered* lists of scalars indexed by number, starting with 0 and with negative subscripts counting from the end. One of the main features of arrays (compared to hashes) is that you have full control over the order in which the elements are inserted. Many algorithms rely on this order (look e.g. at the GD::Graph module). My statement was far too general, what I should have said was to have a unsorted array of 1000 or more elements when your problem requires finding the max or min of that list is not a good design. -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: find the lowest number?
on Sat, 31 Aug 2002 04:30:34 GMT, [EMAIL PROTECTED] (Sudarshan
Raghavan) wrote:
My statement was far too general, what I should have said was to
have a unsorted array of 1000 or more elements when your problem
requires finding the max or min of that list is not a good design.
Again, I beg to differ. I'll use the same example (GD::Graph) to
explain myself.
Say you want to graph a mathematical function
y = f(x)
for 0 = x = 1000.
GD::Graph wants two arrayrefs, so you do:
my ($x, $y);
for (0..1000) {
$x-[$_] = $_;
$y-[$_] = f($_);
}
To have a nice looking graph, you want to have the top/bottom
coincide with the max/min value of your function, so you need to
calculate ymax and ymin, which, of course, you do in the same for
loop that generates the (x,y) pairs.
--
felix
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Re: find the lowest number?
David Samuelsson wrote at Fri, 30 Aug 2002 10:22:56 +0200: i get an array conataining a lot off numbers like this: 567 551 540 540 540 533 531 526 493 476 468 429 421 520 how do i find the lowest or the higest number in this series? There's also a module doing such a job for you: use List::Util qw/min max/; my $min = min @array; my $max = max @array; (Of course, that's not the quickest solution, as it is an 2 * O(n) algorithm, and perhaps also a sort is quicker for little lists, as it is implemented directly in Perl - But it's a very simple and readable solution). Greetings, Janek -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: find the lowest number?
Felix Geerinckx wrote: snip For small array sizes, it doesn't matter which method you use, since the cpu time will be near zero anyway. For larger sizes it does matter, and the loop method is a clear winner. Therefor, imho, your suggestion in March (and mine now :-) to use a loop, is *always* preferable. *Always* is a very strong word :). For small array sizes the method may make a difference if you're going to be performing the operation many times. Sudarshan's banchmark called sort twice and reverse once when it only needed to call sort once, and it was still much faster than the linear scan for an array with seven elements. If you had an application that spent most of its time finding the minimum and maximum element of small collections the sort method would be preferable. It's also idiomatic (didn't Randall Schwartz post about this once saying it was an example in the Llama book?) and imho quite readable. There are other situations in which you might prefer a log n to a linear algorithm for this kind of thing. If you need to repeatedly find minimum and maximum elements of a collection over a period in which insertions and deletions are being performed you might want to keep the collection sorted. Likewise if you collect the elements over time and want to amortize the cost of the operation. If your data is too large to fit in memory a log n algorithm may beat a linear algorithm badly for all reasonable values of n if the linear algorithm uses a lot of disk seeks. Without knowing the details of the application it's not possible to know what algorithm is best. I suspect that a lot of the people who ask this question are dealing with small arrays, in which case the sort solution makes sense. It's also kind of cool :). But the caveat about large arrays _is_ important- don't want people using it on an array with fifty-million elements! (Of course if you're trying to maximize performance working with large datasets you might be best off using C or Lisp anyway, or using an RDBMS to do your heavy lifting- and hopefully you're not dealing with these kinds of datasets if you're at the stage where you're first learning how to find the maximum element of an array). This (how do I find the greatest/lowest element?) comes up every few months. Maybe there should be a list faq that covers this and other questions that get asked a lot and aren't in the Perl faq :). Tagore Smith -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
