Using map to Add a Line Breaks to a List

goober99 has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Using map to Add a Line Breaks to a List by Aristotle (Chancellor) on Mar 05, 2005 at 05:54 UTC
The direct fix: `print map { /(.+)\./ && "$1\n" } sort RetrieveIllustrationList( $cl_us +erinput );` [download] The subtle fix (my recommendation): `print map { /(.+)\./, "\n" } sort RetrieveIllustrationList( $cl_userin +put );` [download] Doing a lot of extra work with a dash of join: `print join "\n", map( /(.+)\./, sort RetrieveIllustrationList( $cl_use +rinput ) ), '';` [download] Letting print do the work with an implicit version of the subtle fix (probably the most efficient, but caveat microoptimizer): `local $, = "\n"; print map( /(.+)\./, sort RetrieveIllustrationList( $cl_userinput ) ), + '';` [download] Suboptimal variations with a double loop: `print map "$_\n", map /(.+)\./, sort RetrieveIllustrationList( $cl_use +rinput ); print "$_\n" for map /(.+)\./, sort RetrieveIllustrationList( $cl_user +input );` [download] I think that's enough for tonight. Makeshifts last the longest.	[reply] [d/l] [select]
Re^2: Using map to Add a Line Breaks to a List by goober99 (Scribe) on Mar 05, 2005 at 06:07 UTC
I like your recommended subtle fix. I like the elegant perlishness about it. I think I may edit my code to use it. I don't understand how it works though. Can someone explain?	[reply]
Re^3: Using map to Add a Line Breaks to a List by Aristotle (Chancellor) on Mar 05, 2005 at 08:04 UTC
As !1 explained: a successful pattern match in list context returns a list of captured matches, or an empty list if it didn't match. That's why your own `map { /(.+)\./ }` works — map provides list context to the block, so the pattern match returns the captured text. What I did is simply unconditionally add a `"\n"` to that list. So if the list was `"foo.txt", "bar.bmp", "baz.pdf"` [download] then the result is `"foo", "\n", "bar", "\n", "baz", "\n"` [download] which prompts print to duly produce the desired result. Makeshifts last the longest.	[reply] [d/l] [select]
Re^3: Using map to Add a Line Breaks to a List by !1 (Hermit) on Mar 05, 2005 at 06:17 UTC
It's due to the capturing regex in list context. This returns a list of captured strings. Map then passes this list and the "\n" to print. Since $, = $\ = "", your output works the way it does. Of course, this will print blank lines if your filename doesn't contain a period.	[reply]
Re^4: Using map to Add a Line Breaks to a List by Aristotle (Chancellor) on Mar 05, 2005 at 07:56 UTC
Re: Using map to Add a Line Breaks to a List by bobf (Monsignor) on Mar 05, 2005 at 05:27 UTC
You're using the m// in scalar context, so it is returning true on success instead of your captured text (see perlop). Separate the two statements: `print map { m/(.+)/; $1 . "\n" } sort @array;` [download] You could use a join in there, too.	[reply] [d/l]
Re: Using map to Add a Line Breaks to a List by saintmike (Vicar) on Mar 05, 2005 at 05:22 UTC
I bet you meant to say you don't understand why this is. Just in case: it's because the return value of `/(.+)\./` in case of a match is a list with a single element: The item matched between the parentheses. On the other hand, the return value of `/(.+)\./ . "\n"` is "1\n" because the dot puts the regex in scalar context, in which case it returns true (1) or false (""). You could work around it by putting a `map { "$_\n" }` in front of your map.	[reply] [d/l] [select]
Re: Using map to Add a Line Breaks to a List by artist (Parson) on Mar 05, 2005 at 05:36 UTC
`@files = ('hello.txt', 'perl.bmp'); print join "\n", map { s/(.+)\..+$/$1/;$_} @files;` [download]	[reply] [d/l]
Re: Using map to Add a Line Break to a List by goober99 (Scribe) on Mar 05, 2005 at 05:36 UTC
Thank you for your replies. saintmike, I did understand why, I just didn't know an easy workaround, but your explanation was very clear. I went by the solution bobf and lidden suggested. I liked being able to do it without adding another map. I assume not having to loop again would make it a miniscule fraction of a millisecond faster.	[reply]
Re: Using map to Add a Line Breaks to a List by lidden (Curate) on Mar 05, 2005 at 05:32 UTC
Untested but i think this should work: `print map {/(.+)\./ ; $1 . "\n"} sort(RetrieveIllustrationList($cl_use +rinput));` [download]	[reply] [d/l]
Re: Using map to Add a Line Breaks to a List by graff (Chancellor) on Mar 05, 2005 at 18:12 UTC
How odd that no one has suggested this yet: `print map { s/\..*/\n/; $_ } sort(RetrieveIllustrationList($cl_userinp +ut));` [download]	[reply] [d/l]
Re: Using map to Add a Line Breaks to a List by iblech (Friar) on Mar 06, 2005 at 10:17 UTC
`print map { (/(.+)\./)[0] . "\n" } sort(RetrieveIllustrationList($cl_userinput));` --Ingo	[reply] [d/l]