Matthew,
Excellent comments. You described exactly the effect I was going for,
and also perfectly described the kind of conundrums that can take place
when doing something like this. Since I was going for quotes, then
commas, then spaces only if no commas existed, I have modified the code
Ezra so kindly provided to look like this:
def parse_tags(input)
tags = []
# pull out the quoted tags
input.gsub!(/"(.*?)"/ ) { tags << $1; “” }
#pull out comma separated tags
if input.include? “,”
#find all tags that end with comma - ex: tag1,tag2,tag3 ==>
tag1,tag2,
input.gsub!(/(.+?),/) { tags << $1; “” }
#find all tags that begin with a comma - ex: tag1, tag2, tag3 ==> ,
tag2 , tag3
input.gsub!(/,(.+?)/) { tags << $1; “” }
tags << input
else
tags.concat input.split(/\s/)
end
# get whatever's left
# tags.concat input.split(/,/)
# strip whitespace from the names
tags.map! { |t| t.strip }
# delete any blank tag names
tags = tags.delete_if { |t| t.empty? }
return tags
end
#below is to test the function
puts parse_tags (‘“jay” hello mary, goodbye stranger, its been long,
“hello again”’)
You’ll notice the if else end section which looks for commas, and then
decides to split tags by either commas, or spaces, conditionally
Thanks
Matthew S. wrote:
On Jun 1, 2006, at 21:48, web mail wrote:
Jeff, Ezra,
Thanks tons for the help. You guys both helped a lot. My only question
so far, for Ezra, is this: My second tag is “second tag”, not in
quotes,
but with a space between the two words. The tag IS meant to be two
words
long. So I’m thinking that if you replace all the commas with spaces,
wont that split my second tag into two tags, when it was meant to be
just one tag ?
You’re right, that’s what would happen. The problem is that in the
case where a non-quoted multi-word tag (second tag) occurs in the
same input as two space-delimited single-word tags (third_tag
fourth_tag), you’re out of luck. This isn’t a problem that’s
solvable without some sort of semantic knowledge, potentially quite a
bit of it. For example, how would you distinguish between (“first
tag”, second tag, dog pile) and (“first tag”, second tag, dog pile)
where (dog pile) is meant as one and two tags, respectively?
The tags can appear in any order, and they can either be quoted,
separated by commas, or separated by spaces. I’ve decided that in the
case of all three, i would like quotes to have precedence, followed by
commas, followed by spaces. so, for an example, the following string:
I think that you’re using ‘precedence’ in a way that’s not quite
formally correct. Commas don’t have precedence over spaces in the
same way that * has precendence over +. From your examples, a more
accurate description might be: if commas occur outside of a quoted
tag, assume that tags are comma-delimited; otherwise, assume that
tags are space-delimited.
EXACTLY what i meant.
Even that, though, leaves you with a bit of a problem making the dog-
pile decision, if it’s the only input. Is it meant as a single tag
in a comma-delimited list (convention being to leave off the final
delimiter in lists)? Or is it meant as two tags in a space-delimited
list? It’s still ambiguous as to what the user’s intention might
have been without delving into some sort of semantics.
Another poster (can’t remember whom) interpreted your specification
as “after the last comma, assume things are space-delimited”, which
might also be an option.
For reasons of simplicity (for the user - you’re free to make your
job as hard as you please!), though, I’d suggest that it would be
best to stick to a single type of delimiter. I prefer spaces,
myself, since tags tend to be single words, and people are used to
that sort of input (not only from the canonical examples of flickr or
del.icio.us, but because it mimics search engines, for instance).
Matthew S.
[1] “Dog pile” in this sense: http://en.wikipedia.org/wiki/Pile-on
which I thought of because, being the oldest and largest of all my
cousins and siblings, it was always my misfortune to be on the bottom.