Re^2: Convert a string into a hash

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Re^3: Convert a string into a hash by ikegami (Patriarch) on Aug 15, 2009 at 02:18 UTC
Conditional `my` isn't allowed. Besides, your code doesn't compile. You want `my %code = do { my $i = 0; map { $_ => $i++ } split /,/, $tokens };` [download] If you really want no explicitely declared temp variables, you can use the following: `my %code = sub { map { $_[$_] => $_ } 0..$#_ }->( split /,/, $tokens ) +;` [download] But honestly, there's no need to limit the scope that badly. Either of the following are quite suitable: `my $i = 0; my %code = map { $_ => $i++ } split /,/, $tokens;` [download] `my @code = split /,/, $tokens; my %code = map { $code[$_] => $_ } 0..$#code;` [download]	[reply] [d/l] [select]
Re^4: Convert a string into a hash by vitoco (Hermit) on Aug 15, 2009 at 03:34 UTC
Conditional `my` isn't allowed. Besides, your code doesn't compile. Yes, it does... without `use strict;` !!! Thanks for point that out.	[reply] [d/l] [select]
Re^5: Convert a string into a hash by ikegami (Patriarch) on Aug 15, 2009 at 15:48 UTC
Fine, it compiles without strict but it has two additional errors. It's not using strict :) Package var `$i` is used when you intended lexical `$i` to be used. Why bother declaring lexical `$i` if you're not going to use it and you're ok with using the (unlocalised!!!) package var? Your code is equivalent to `my %code = map { $_ => $i++ } split /,/, $tokens; my $i = 0` [download] so you should use the following is you think it's fine `my %code = map { $_ => $i++ } split /,/, $tokens;` [download]	[reply] [d/l] [select]
Re^6: Convert a string into a hash by vitoco (Hermit) on Aug 15, 2009 at 16:56 UTC
Re^3: Convert a string into a hash by Your Mother (Archbishop) on Aug 14, 2009 at 23:20 UTC
I can see how you can do that but not why you'd want to do it. The array is sorted already. There is no information in a hash with index values that isn't in an array. So, unless I'm missing something, it buys you nothing except a speed penalty and obfuscates a simple operation/need. If you could explain what you're going to do with it in the end, you might get some more interesting answers approaches. :)	[reply]
Re^4: Convert a string into a hash by ikegami (Patriarch) on Aug 15, 2009 at 02:25 UTC
There is no information in a hash with index values that isn't in an array. Yes and no. If you want to know "the position of a given number", the information is there in the array, but finding it is hard (O(N)). It's O(1) with a hash. `my ($index) = grep $code[$_] == $x, 0..$#code; -vs- my $index = $code{$x};` [download]	[reply] [d/l]
Re^5: Convert a string into a hash by Your Mother (Archbishop) on Aug 15, 2009 at 04:27 UTC
NIce comparison/example of a possible why. With `List::Util::first`, or equivalent code, you could at least move the array more to the middle ground (on average); I know you know that already and it's good (for me at least) to be confronted with the algorithm costs. That alone suggests a reason for doing it with the hash.	[reply] [d/l]
Re^6: Convert a string into a hash by ikegami (Patriarch) on Aug 15, 2009 at 15:52 UTC
Re^4: Convert a string into a hash by vitoco (Hermit) on Aug 15, 2009 at 03:19 UTC
I'm sorry for not being so clear. English is not my native language, so I decided just to write the code in the usual way with a minimum of info about the context. I thought this thread as a perl coding hackers topic. BTW, my best code really was: `my %code = (my $i = 0 or map {($_, $i++)} split(/,/, $tokens));` The previous was an updated one using `=>` instead of the subarray, a more elegant code based on your reply, but I didn't notice my mistake when I pasted the line.	[reply] [d/l] [select]
Re^5: Convert a string into a hash by roboticus (Chancellor) on Aug 15, 2009 at 13:04 UTC
vitoco: Yes, it's a perl coding hackers topic. But what Your Mother was trying to convey is that you might be focused too tightly on the details. Sure, we can help you get an answer to your question....but you might be asking the wrong question. Example: Suppose you're walking through the woods trying to get to Grandmother's house. The path branches several times here and there, and you're worried about getting lost. So you're walking along the path, and you find a ravine in your path, and the rope bridge across it is broken. So now you're trying to cross the ravine. You successfully make rope by weaving together tree bark, and you're trying to build a new rope bridge. But you're having trouble trying to lasso a stump on the other side of the ravine. So you use your magic whistle to call a helpful mystical owl from the sky and ask it "How can I lasso the stump over there?". The owl will happily try to help you construct your rope bridge. But if you happened to phrase your question as "Hi, I'm trying to get to Grandmother's house, but this ravine is in my way. I'm trying to figure out how to cross it. Now I've made this rope, and I think all I need to do is lasso that stump so I can cross this ravine. Can you help?" Then the owl could offer, "Well, I can help you cross the ravine. But if you're trying to get to Grandmother's house, it would be much simpler to go back two intersections and take a left, take your next right at the large rock, and it's about 100 yards further." In other words, by focusing in on the smaller problems (as we programmers are often wont to do), you may have created an artificial problem for yourself to solve, when simpler and more direct solutions are available. If don't give us enough information, we'll try to help you cross the ravine, but if you give us some context of what you're trying to accomplish, we might be able to direct you to the already created Grandmother::House module or some such. ...roboticus in a somewhat whimsical mood.	[reply]