Beefy Boxes and Bandwidth Generously Provided by pair Networks
Your skill will accomplish
what the force of many cannot
 
PerlMonks  

Re: What’s the best way to get the last N elements of a Perl array?

by linuxer (Deacon)
on Apr 20, 2009 at 11:29 UTC ( #758676=note: print w/ replies, xml ) Need Help??


in reply to What’s the best way to get the last N elements of a Perl array?

If undef is no valid entry in your array, you could use your solution and grep the defined values from your slice result.

@last_n = grep { defined $_ } @source[ -$n .. -1 ];

Update:

As svenXY mentioned: my solution does not work! :o(

$ perl -wle '@a = 1..3; @b = grep { defined $_ } @a[-4 .. -1]; print " +<$_>" for @b;' Modification of non-creatable array value attempted, subscript -4 at - +e line 1. $ perl -wle '@a = 1..3; @b = @a[-4 .. -1]; @b = grep {defined $_} @b; +print "<$_>" for @b;' <1> <2> <3>

Can someone please enlighten me, what's the problem with my attempt?

2nd Update:

During my research I found an explanation in Modification of non-creatable array value attempted (it's a slightly other topic, but at least the same error message) and grep's perldoc.

I came to the conclusion, that the error is thrown, because grep tries to alias the list values; and this fails for not existent array elements.


Comment on Re: What’s the best way to get the last N elements of a Perl array?
Select or Download Code
Replies are listed 'Best First'.
Re^2: What’s the best way to get the last N elements of a Perl array?
by svenXY (Deacon) on Apr 20, 2009 at 11:40 UTC
    nope, does not work for me: Modification of non-creatable array value attempted, subscript -9 at array_ende.pl line 23.
    whereas it does work as a two-liner (see above)
    Regards,
    svenXY

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://758676]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others rifling through the Monastery: (10)
As of 2015-07-07 18:58 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









    Results (93 votes), past polls