Split string suppressing all null fields - ruby

Question

I want to split a string suppressing all null fields
Command:
",1,2,,3,4,,".split(',')
Result:
["", "1", "2", "", "3", "4", ""]
Expected:
["1", "2", "3", "4"]
How to do this?
Edit
Ok. Just to sum up all that good questions posted.
What I wanted is that split method (or other method) didn't generate empty strings. Looks like it isn't possible.
So, the solution is two step process: split string as usual, and then somehow delete empty strings from resulting array.
The second part is exactly this question
(and its duplicate)
So I would use
",1,2,,3,4,,".split(',').delete_if(&:empty?)
The solution proposed by Nikita Rybak and by user229426 is to use reject method. According to docs reject returns a new array. While delete_if method is more efficient since I don't want a copy. Using select proposed by Mark Byers even more inefficient.
steenslag proposed to replace commas with space and then use split by space:
",1,2,,3,4,,".gsub(',', ' ').split(' ')
Actually, the documentation says that space is actually a white space. But results of "split(/\s/)" and "split(' ')" are not the same. Why's that?
Mark Byers proposed another solution - just using regular expressions. Seems like this is what I need. But this solution implies that you have to be a master of regexp. But this is great solution! For example, if I need spaces to be separators as well as any non-alphanumeric symbol I can rewrite this to
",1,2, ,3 3,4 4 4,,".scan(/\w+[\s*\w*]*/)
the result is:
["1", "2", "3 3", "4 4 4"]
But again regexps are very unintuitive and they need an experience.
Summary
I expect that split to work with whitespaces as if whitespaces were a comma or even regexp. I expect it to do not produce empty strings. I think this is a bug in ruby or my misunderstanding.
Made it a community question.

Answer 1

There's a reject method in Array:
",1,2,,3,4,,".split(',').reject { |s| s.empty? }
Or if you prefer Symbol#to_proc:
",1,2,,3,4,,".split(',').reject(&:empty?)

Answer 2

Hoping to illuminate a bit here:
But results of "split(/\s/)" and "split(' ')" are not the same. Why's that?
If you look at the docs for String#split you'll see that split with ' ' is a special case:
If pattern is a single space, str is split on whitespace,
with leading whitespace and runs of contiguous whitespace characters ignored.
You also mention:
I expect it to do not produce empty strings. I think this is a bug in ruby or my misunderstanding.
The problem probably lies between the keyboard and the chair. ;-)
split will happily produce empty strings as it should, because there are times when you would definitely want this ability, and there are plenty of easy ways to work around it. Consider if you were splitting a csv from an Excel file. Anywhere you see ',,' would be an empty column, not a column you should just get rid of.
Regardless, you've seen a bunch of solutions - and here's another one that might show you the things you can do with ruby and split!
It seems you want to split up data between multiple commas, so why not try that and see what happens?
a = ",1,2,,3,4,,5,,,,6,,,".split(/,+/)
It's a simple enough regular expression: /,+/ means one or more commas, so we'll split on that.
This almost gives you want you want, except that you also want to ignore the leading empty field. You'll note that split ignores the empty field on the end because (from the String#split docs):
If the limit parameter is omitted, trailing null fields are suppressed.
So that means we can either use something that will remove that nil at the front of the array or just remove the initial commas. We can use gsub for that:
a = ",1,2,,3,4,,5,,,,6,,,".gsub(/^,+/,'')
If you print that out you'll see that our trailing empty "field" is now gone. So we can combine them all in one line:
a = ",1,2,,3,4,,5,,,,6,,,".gsub(/^,+/,'').split(/,+/)
And you have another solution!
And incidentally, this points out another possibility, that we can just cleanup our string entirely before sending it to split if we want a simple split. I'll leave it to you to figure out what this one is doing:
a = ",1,2,,3,4,,5,,,,6,,,".gsub(/,+/,',').gsub(/^,/,'').split(',')
There's lots of ways to do things in ruby. If it seems that ruby isn't doing what you want, then take a look at the docs and realize that it probably works the way that it does for a reason (there are plenty of people who would be upset if split wasn't able to spit out empty fields :)
Hope that helps!

Answer 3

You could use split followed by select:
",1,2,,3,4,,".split(',').select{|x|!x.empty?}
Or you could use a regular expression to match what you want to keep instead of splitting on the delimiter:
",1,2,,3,4,,".scan(/[^,]+/)

Answer 4

",1,2,,3,4,,".split(/,/).reject(&:empty?)
",1,2,,3,,,4,,".squeeze(",").sub(/^,*|,*$/,"").split(",")

Answer 5

String#split(pattern) behaves as desired when pattern is a single space (ruby-doc).
",1,2,,3,4,,".gsub(',', ' ').split(' ')