Type of arg 1 to splice must be array (not keys)

jeanluca has asked for the wisdom of the Perl Monks concerning the following question:

Dear monks

I want a subset of the keys I have in an hash. I tried the following:

splice( keys(%mh), 0, 100 ) ;
[download]

Which didn't work, it returned:

Type of arg 1 to splice must be array (not keys) at myprog.pl line 36,
+ near "100)"
Compilation failed in require at ./test.pl line 8.
BEGIN failed--compilation aborted at ./test.pl line 8.
[download]

I can fix this like

my @k = keys(%mh) ;
splice( @k ...) ;
[download]

but I guess the one-liner should work too ?!
Any suggestions ?

cheers
LuCa

Update: thnx JavaFan, thats it, although I have doubts now about the order of keys :)

Comment on Type of arg 1 to splice must be array (not keys) Select or Download Code

Replies are listed 'Best First'.
Re: Type of arg 1 to splice must be array (not keys) by jwkrahn (Abbot) on Dec 14, 2009 at 12:57 UTC
Try it using a list slice: `my @k = ( keys %mh )[ 0 .. 99 ];` [download]	[reply] [d/l]
Re^2: Type of arg 1 to splice must be array (not keys) by jeanluca (Deacon) on Dec 14, 2009 at 13:11 UTC
Thats a good solution. The only problem is that I don't know the number of keys. So I can have more or less. Which means I have to rewrite your solution to `my @k = (keys %mh)[0 .. (scalar keys(%my) <= 100 ? scalar keys(%mh) : +100)] ;` [download] Which doesn't look that good anymore. So I prefer 'splice'. Is there a way to convert this 'key' list into an array ?	[reply] [d/l]
Re^3: Type of arg 1 to splice must be array (not keys) by JavaFan (Canon) on Dec 14, 2009 at 13:15 UTC
`splice @{[keys %mh]}, 0, 100;` [download]	[reply] [d/l]
Re^3: Type of arg 1 to splice must be array (not keys) by ikegami (Patriarch) on Dec 14, 2009 at 15:36 UTC
Your slice solution is buggy and uses `scalar` needlessly. `my $keys = keys(%my) < 100 ? keys(%mh) : 100; my @k = ( keys %mh )[0..$keys-1];` [download] or `my $keys = min 100, keys(%mh); my @k = ( keys %mh )[0..$keys-1];` [download] (List::Util provides `min`) A `splice` solution: `my @k = keys %mh; splice( @k, 100 ) if @k > 100;` [download] You need the conditional to avoid the warning. Update: Added fix to OP's slice solution.	[reply] [d/l] [select]
Re: Type of arg 1 to splice must be array (not keys) by AnomalousMonk (Archbishop) on Dec 14, 2009 at 13:14 UTC
I don't understand what you are trying to do. The statement `splice( keys(%mh), 0, 100 ) ;` suggests you want to remove the first 100 keys from the hash. However, a hash does not have a 'first n keys': 'first' implies order, and a hash does not have 'ordered' keys. The statement `my @k = keys(%mh) ;` gives you all the keys of the hash in essentially random order.	[reply] [d/l] [select]
Re^2: Type of arg 1 to splice must be array (not keys) by jeanluca (Deacon) on Dec 14, 2009 at 13:21 UTC
I hope to get any order when I use Tie::IxHash I guess splice returns the removed elements, right ? So when I do something like `...... grep { ... } splice( keys(%my),0,100 ) ;` [download]	[reply] [d/l]
Re: Type of arg 1 to splice must be array (not keys) by happy.barney (Friar) on Dec 14, 2009 at 15:31 UTC
why splice ? :-) `my $max = 100; my @list = grep $max-- > 0, keys %hash;` [download]	[reply] [d/l]
Re^2: Type of arg 1 to splice must be array (not keys) by kikuchiyo (Hermit) on Dec 14, 2009 at 22:29 UTC
If you format that like this: `$max --> 0` it looks like as if there was a "$max goes to zero" operator. A great way to confuse anybody who reads your code.	[reply] [d/l]
Re^3: Type of arg 1 to splice must be array (not keys) by ikegami (Patriarch) on Dec 14, 2009 at 23:12 UTC
Would you prefer `--$max >= 0`?	[reply] [d/l]