Best way to copy an array?

John M. Dlugosz has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Best way to copy an array? by jweed (Chaplain) on Feb 22, 2004 at 06:22 UTC
For non-huge arrays, this should work fine: `@newlist = @{$self->{oldlist}};` [download] This will copy the elements but not alias them: i.e., it will make 2 separate arrays that happen to start out with the same elements. Code is (almost) always untested. http://www.justicepoetic.net/	[reply] [d/l]
•Re: Best way to copy an array? by merlyn (Sage) on Feb 22, 2004 at 12:07 UTC
For a more detailed treatment on this, see my article on deep copying. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re: Best way to copy an array? by BrowserUk (Patriarch) on Feb 22, 2004 at 12:27 UTC
If there is any chance that the elements of your array are themselves compound (ie. array or hashes), then you may like to look at Clone. It's much quicker than any pure perl method, and it doesn't get confused by deeply nested structures. Examine what is said, not who speaks. "Efficiency is intelligent laziness." -David Dunham "Think for yourself!" - Abigail Timing (and a little luck) are everything!	[reply]
Re: Best way to copy an array? by NetWallah (Canon) on Feb 22, 2004 at 07:03 UTC
`@newlist= @{$self->{oldlist}}; # Direct copy #Alternative ... push @newlist, @{$self->{oldlist}}; # Stuff it in` [download] "Experience is a wonderful thing. It enables you to recognize a mistake when you make it again."	[reply] [d/l]
Re: Best way to copy an array? by blokhead (Monsignor) on Feb 22, 2004 at 06:56 UTC
assignments made to the copy don't affect the original, but the elements reference the same things initially. Am I missing something? What exactly is wrong with `@newlist = @{$self->{oldlist}};`? What do you mean by "reference the same things initially?" Is this an array of references? Maybe you mean something like `@newlist = map { [ @$_ ] } @{ $self->{oldlist} }; @newlist = map { { %$_ } } @{ $self->{oldlist} };` [download] but it's hard to tell.. blokhead	[reply] [d/l] [select]
Re: Re: Best way to copy an array? by John M. Dlugosz (Monsignor) on Feb 23, 2004 at 04:37 UTC
Am I missing something? What exactly is wrong with `@newlist = @{$self->{oldlist}};`? I thought that doesn't copy anything, but aliases the array. You mean I'm copying a list every time I dereference it?! No, 'cause `push @{$self->{oldlist}}, $x` does indeed modify the thing being remembered by self. Ah, assigning to a @list naturally copies the elements and keeps the identity of the left-hand-side. That makes sence. Thanks, —John	[reply] [d/l] [select]
Re: Best way to copy an array? by flyingmoose (Priest) on Feb 22, 2004 at 23:50 UTC
Oooh! Oooh! I know this one... `memcpy()` [download] Oh wait, wrong language. Darn. (edit: not like I care, but easy with the modpoints guys -- it's a joke! -- memcpy is one of my favorite C commands -- very useful, and I abuse it often.)	[reply] [d/l]