FAQ 4.8 How do I perform an operation on a series of integers?

This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

------------------------------------------------------------ --------

4.8: How do I perform an operation on a series of integers?

To call a function on each element in an array, and collect the results,
use:

@results = map { my_func($_) } @array;

For example:

@triple = map { 3 * $_ } @single;

To call a function on each element of an array, but ignore the results:

foreach $iterator (@array) {
some_func($iterator);
}

To call a function on each integer in a (small) range, you can use:

@results = map { some_func($_) } (5 .. 25);

but you should be aware that the ".." operator creates an array of all
integers in the range. This can take a lot of memory for large ranges.
Instead use:

@results = ();
for ($i=5; $i < 500_005; $i++) {
push(@results, some_func($i));
}

This situation has been fixed in Perl5.005. Use of ".." in a "for" loop
will iterate over the range, without creating the entire range.

for my $i (5 .. 500_005) {
push(@results, some_func($i));
}

will not create a list of 500,000 integers.



------------------------------------------------------------ --------

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Re: FAQ 4.8 How do I perform an operation on a series of integers?

On Sep 20, 9:03 pm, PerlFAQ Server wrote:
> This is an excerpt from the latest version perlfaq4.pod, which
> comes with the standard Perl distribution. These postings aim to
> reduce the number of repeated questions as well as allow the community
> to review and update the answers. The latest version of the complete
> perlfaq is athttp://faq.perl.org.
>
> ------------------------------------------------------------ --------
>
> 4.8: How do I perform an operation on a series of integers?
>
> To call a function on each element in an array, and collect the results,
> use:
>
> @results = map { my_func($_) } @array;
>
> For example:
>
> @triple = map { 3 * $_ } @single;
>
> To call a function on each element of an array, but ignore the results:
>
> foreach $iterator (@array) {
> some_func($iterator);
> }
>
> To call a function on each integer in a (small) range, you can use:
>
> @results = map { some_func($_) } (5 .. 25);
>
> but you should be aware that the ".." operator creates an array of all
> integers in the range. This can take a lot of memory for large ranges.
> Instead use:
>
> @results = ();
> for ($i=5; $i < 500_005; $i++) {
> push(@results, some_func($i));
> }

I have not seen this before. What is the purpose of the "_" in 500_005
or is it just used to replace 500,005?

Bill H

Re: FAQ 4.8 How do I perform an operation on a series of integers?

On Thu, 20 Sep 2007 18:08:00 -0700, Bill H wrote:

>On Sep 20, 9:03 pm, PerlFAQ Server wrote:
>> This is an excerpt from the latest version perlfaq4.pod, which
>> comes with the standard Perl distribution. These postings aim to
>> reduce the number of repeated questions as well as allow the community
>> to review and update the answers. The latest version of the complete
>> perlfaq is athttp://faq.perl.org.
>>
>> ------------------------------------------------------------ --------
>>
>> 4.8: How do I perform an operation on a series of integers?
>>
>> To call a function on each element in an array, and collect the results,
>> use:
>>
>> @results = map { my_func($_) } @array;
>>
>> For example:
>>
>> @triple = map { 3 * $_ } @single;
>>
>> To call a function on each element of an array, but ignore the results:
>>
>> foreach $iterator (@array) {
>> some_func($iterator);
>> }
>>
>> To call a function on each integer in a (small) range, you can use:
>>
>> @results = map { some_func($_) } (5 .. 25);
>>
>> but you should be aware that the ".." operator creates an array of all
>> integers in the range. This can take a lot of memory for large ranges.
>> Instead use:
>>
>> @results = ();
>> for ($i=5; $i < 500_005; $i++) {
>> push(@results, some_func($i));
>> }
>
>I have not seen this before. What is the purpose of the "_" in 500_005
>or is it just used to replace 500,005?
>
>Bill H

Yeah, thats interresting

"for ($i=5; $i < 500_005; $i++)"

between 500 o' 5
or between 5-500,005, thats interresting

Re: FAQ 4.8 How do I perform an operation on a series of integers?

Bill H wrote:
> On Sep 20, 9:03 pm, PerlFAQ Server wrote:
>>
>> @results = ();
>> for ($i=5; $i < 500_005; $i++) {
>> push(@results, some_func($i));
>> }
>
> I have not seen this before. What is the purpose of the "_" in 500_005
> or is it just used to replace 500,005?

perldoc perldata

[ SNIP ]

Scalar value constructors

Numeric literals are specified in any of the following floating point or
integer formats:

12345
12345.67
.23E-10 # a very small number
3.14_15_92 # a very important number
4_294_967_296 # underscore for legibility
0xff # hex
0xdead_beef # more hex
0377 # octal (only numbers, begins with 0)
0b011011 # binary

You are allowed to use underscores (underbars) in numeric literals between
digits for legibility. You could, for example, group binary digits by
threes (as for a Unix-style mode argument such as 0b110_100_100) or by
fours (to represent nibbles, as in 0b1010_0110) or in other groups.



John
--
Perl isn't a toolbox, but a small machine shop where you
can special-order certain sorts of tools at low cost and
in short order. -- Larry Wall