Remove a specific element from an Array
Sumit
I am a new bie to this Group.
I have a Problem.
I want to remove an element from an array whose index i dont know.
--------------------------------------------------------------------------------------------------
#!/usr/bin/perl -w
use strict;
my @updateNames = ();
my @tempArr = ();
my $item = "";
my $item2 = "";
push @updateNames,"I_love_you";
push @updateNames,"I_love_you_too";
push @updateNames,"I_hate_you";
push @tempArr,"I_love_you";
push @tempArr,"I_love_Him";
push @tempArr,"I_hate_you";
foreach $item (@updateNames)
{
foreach $item2 (@tempArr)
{
if ($item eq $item2)
{
pop @updateNames,$item; #This pop is just removing the
last element i want to remove $item2 from @updateNames
}
}
}
print "\n";
foreach $item (@updateNames)
{
print $item;
print "\n";
}
--------------------------------------------------------------------------------------------------
Can somebody help me on this?
--
Sumit
anno...@radom.zrz.tu-berlin.de
That code doesn't compile. Please *run* your code before you post
it to the group. Non-working code is almost useless as a problem
description.
> Can somebody help me on this?
It looks like you want to remove the elements from @updateNames that
also appear in @tempArr. If so, it would be better to use a hash
instead of @tempArr. You can the use grep() to remove the unwanted
entries:
my @updateNames = qw( I_love_you I_love_you_too I_hate_you);
my %tempHash;
$tempHash{ $_} = 1 for qw( I_love_you I_love_Him I_hate_you);
@updateNames = grep !$tempHash{ $_}, @updateNames;
print "@updateNames\n";
__END__
Anno
Peter Makholm
> I am a new bie to this Group.
> I have a Problem.
> I want to remove an element from an array whose index i dont know.
If you want to remove all elements matching some condition, the you
could use the grep function:
@names = grep { $_ != "Some name" } @names;
If you just want to remove one of the element with some value you'll
have to find the index by searching the list and then use splice to
remove the element.
//Makholm
Sumit
> it to the group. Non-working code is almost useless as a problem
> description.
I can compile the code, the result is wrong i know but i didn't had
any problem in running the code.
Sumit
anno...@radom.zrz.tu-berlin.de
Oh please... . Look at your code again:
#!/usr/bin/perl -w
use strict;
[snip]
foreach $item (@updateNames)
{
The variable $item is undeclared. Under "strict" that is a fatal error.
What do you hope to gain by making verifiably false statements?
Anno
anno...@radom.zrz.tu-berlin.de
Right, apologies. I lost a declaration or two in copy/paste when I
tried to run it.
Anno
Paul Lalli
> I am a new bie to this Group.
> I have a Problem.
> I want to remove an element from an array whose index i dont know.
Loop through the array, find the index. Use splice()
my $index;
for my $i (0..$#stuff) {
if ($stuff[$i] eq 'RemoveThis') {
$index = $i;
last;
}
}
splice(@stuff, $index, 0);
perldoc -f splice
for more information
Of course, the real answer to the problem is that you should have been
using a hash to begin with. That is, rather than:
my @stuff = ('foo', 'bar', 'baz');
You should have
my %stuff = (foo => 1, bar => 1, baz => 1);
so that when it comes time to remove "bar", all you have to do is:
delete $stuff{bar};
Paul Lalli
Jürgen Exner
> I want to remove an element from an array whose index i dont know.
> foreach $item2 (@tempArr) {
> if ($item eq $item2) {
> pop @updateNames,$item; #This pop is just removing the
> last element i want to remove $item2 from @updateNames
It is a very bad idea to modify an array (add/remove elements) while you are
looping through it.
> Can somebody help me on this?
This looks like from @updateNames you want to remove all elements where the
value appears in @tempArr.
Have a look at "perldoc -q intersection":
How do I compute the difference of two arrays? How do I compute the
intersection of two arrays?
jue
Sumit
> This looks like from @updateNames you want to remove all elements where the
> value appears in @tempArr.
Yes you are right.
I want to remove all the element of @tempArr if tehy are present in
@updateNames.
> Have a look at "perldoc -q intersection"
sumit: perldoc -q intersection
No documentation found for "perlfaq1".
No documentation found for "perlfaq2".
No documentation found for "perlfaq3".
No documentation found for "perlfaq4".
No documentation found for "perlfaq5".
No documentation found for "perlfaq6".
No documentation found for "perlfaq7".
No documentation found for "perlfaq8".
No documentation found for "perlfaq9".
> How do I compute the difference of two arrays? How do I compute the
> intersection of two arrays?
Searching....
Thanks
Sumit
Paul Lalli
> > Have a look at "perldoc -q intersection"
>
> sumit: perldoc -q intersection
> No documentation found for "perlfaq1".
> No documentation found for "perlfaq2".
> No documentation found for "perlfaq3".
> No documentation found for "perlfaq4".
> No documentation found for "perlfaq5".
> No documentation found for "perlfaq6".
> No documentation found for "perlfaq7".
> No documentation found for "perlfaq8".
> No documentation found for "perlfaq9".
Your installation of Perl is broken. Contact your system
administrator to have them fix it.
> > How do I compute the difference of two arrays? How do I compute the
> > intersection of two arrays?
>
> Searching....
http://perldoc.perl.org/search.html?q=intersection
Paul Lalli
Sherm Pendley
>> Have a look at "perldoc -q intersection"
Who said that? Please don't snip attribution - whether it's for blame or
credit, it's nice to know who deserves it. :-)
> sumit: perldoc -q intersection
> No documentation found for "perlfaq1".
> No documentation found for "perlfaq2".
> No documentation found for "perlfaq3".
> No documentation found for "perlfaq4".
> No documentation found for "perlfaq5".
> No documentation found for "perlfaq6".
> No documentation found for "perlfaq7".
> No documentation found for "perlfaq8".
> No documentation found for "perlfaq9".
Are you using Linux? Some Linux distributions put the Perl docs into a
separate package, such as perl-docs or perl-doc.
Mac OS X does that too - you need to install Xcode to get all the PODs.
sherm--
--
Web Hosting by West Virginians, for West Virginians: http://wv-www.net
Cocoa programming in Perl: http://camelbones.sourceforge.net
Greg Bacon
Sumit <sumit....@gmail.com> wrote:
: I want to remove an element from an array whose index i dont know.
Let's first look at your code from a bottom-up perspective:
: #!/usr/bin/perl -w
: use strict;
This is a good habit. These days, people tend to drop the -w
switch and use the warnings pragma instead, as in
#! /usr/bin/perl
use warnings;
use strict;
: my @updateNames = ();
:
: push @updateNames,"I_love_you";
: push @updateNames,"I_love_you_too";
: push @updateNames,"I_hate_you";
Arrays start out empty, so the assignments aren't strictly necessary.
There are cases where you might want to be explicit for purposes of
emphasis.
In your case, you explicitly set @updateNames to the empty list and
then push values onto it. You can initialize arrays when you declare
them, as in
my @updateNames = (
"I_love_you",
"I_love_you_too",
"I_hate_you",
);
: foreach $item (@updateNames)
: {
: foreach $item2 (@tempArr)
: {
: if ($item eq $item2)
: {
: pop @updateNames,$item;
: }
: }
: }
Someone else already noted (but it doesn't hurt to repeat!) that
you shouldn't modify a collection while you're iterating over it.
The pop operator doesn't work the way you seem to think it does.
(With warnings enabled, you should have seen "Useless use of private
variable in void context" about that line.)
With pop, you supply an array as its only operand, and the result
is that the array's last element (if any) disappears.
: print "\n";
: foreach $item (@updateNames)
: {
: print $item;
: print "\n";
: }
Now from the top-down: at a high level, what are you trying to do?
Do you want to print all elements in @updateNames that are not in
@tempArr? If so, you can simplify your code:
#! /usr/bin/perl
use warnings;
use strict;
my @updateNames = (
"I_love_you",
"I_love_you_too",
"I_hate_you",
);
my %exclude;
$exclude{$_}++ for (
"I_love_you",
"I_love_Him",
"I_hate_you",
);
foreach my $item (@updateNames)
{
print $item, "\n" unless $exclude{$item};
}
As a helpful hint, prefer to search hashes over arrays.
I hope this helps,
Greg
--
This is the golden rule of fractional reserve banking: Do unto
depositors before the depositors do it unto you.
-- Gary North
Petr Vileta
> Hey Guys,
>
> I am a new bie to this Group.
> I have a Problem.
> I want to remove an element from an array whose index i dont know.
> --------------------------------------------------------------------------------------------------
>
> #!/usr/bin/perl -w
> use strict;
>
> my @updateNames = ();
> my @tempArr = ();
> my $item = "";
> my $item2 = "";
>
> push @updateNames,"I_love_you";
> push @updateNames,"I_love_you_too";
> push @updateNames,"I_hate_you";
>
> push @tempArr,"I_love_you";
> push @tempArr,"I_love_Him";
> push @tempArr,"I_hate_you";
>
I rewrote next part of your script
foreach $item (0..$#updateNames)
{
foreach $item2 (@tempArr)
{
if (@updateNames[$item] eq $item2)
{
splice @updateNames, $item, 1;
}
}
}
Maybe this help you ;-)
--
Petr Vileta, Czech republic
(My server rejects all messages from Yahoo and Hotmail. Send me your mail
from another non-spammer site please.)
Tad McClellan
> Sumit wrote:
>> #!/usr/bin/perl -w
> if (@updateNames[$item] eq $item2)
You should not ignore the warnings that perl issues.
They often point out a bug in your code...
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher\100cmdat/"
Petr Vileta
> Petr Vileta <sto...@practisoft.cz> wrote:
>> Sumit wrote:
>
>>> #!/usr/bin/perl -w
>
>> if (@updateNames[$item] eq $item2)
>
>
> You should not ignore the warnings that perl issues.
>
if ($updateNames[$item] eq $item2)
but on my Perl 5.6.1 work well both forms ;-)
Tad McClellan
> Tad McClellan wrote:
>> Petr Vileta <sto...@practisoft.cz> wrote:
>>> Sumit wrote:
>>
>>>> #!/usr/bin/perl -w
>>
>>> if (@updateNames[$item] eq $item2)
>>
>>
>> You should not ignore the warnings that perl issues.
>>
> Well, sorry ;-) Should be
>
> if ($updateNames[$item] eq $item2)
>
> but on my Perl 5.6.1 work well both forms ;-)
Sometimes it doesn't make a difference, but sometimes it does.
See:
perldoc -q difference
What is the difference between $array[1] and @array[1]?
Dr.Ruud
> foreach $item (0..$#updateNames)
> {
> foreach $item2 (@tempArr)
> {
> if (@updateNames[$item] eq $item2)
> {
> splice @updateNames, $item, 1;
I think it is better to undef the array element here,
and then remove the undefined elements by a grep, after the loop.
> }
> }
> }
--
Affijn, Ruud
"Gewoon is een tijger."
anno...@radom.zrz.tu-berlin.de
> Petr Vileta schreef:
>
> > foreach $item (0..$#updateNames)
> > {
> > foreach $item2 (@tempArr)
> > {
> > if (@updateNames[$item] eq $item2)
> > {
> > splice @updateNames, $item, 1;
>
> I think it is better to undef the array element here,
> and then remove the undefined elements by a grep, after the loop.
>
> > }
> > }
> > }
Right. The code above may *seem* to work in some cases but won't
in others. On the other hand, using undef as a marker only works
if the original array elements are all defined. Collecting the
indices and deleting the elements in reverse order after the loop
is a solution, but we have seen better ones in this thread.
Anno