Ruby regular expression

Question

Apparently I still don't understand exactly how it works ...

Here is my problem: I'm trying to match numbers in strings such as:

     910     -6.258000  6.290

That string should gives me an array like this:

[910, -6.2580000, 6.290]

while the string

  blabla9999 some more text 1.1

should not be matched.

The regex I'm trying to use is

/([-]?\d+[.]?\d+)/

but it doesn't do exactly that. Could someone help me ?

It would be great if the answer could clarify the use of the parenthesis in the matching.

Have you considered splitting on whitespace instead?

Dave Newton
– Dave Newton

2011-09-12 12:41:30 +00:00
Commented Sep 12, 2011 at 12:41 — Dave Newton
– Dave Newton, Commented Sep 12, 2011 at 12:41

Roland Mai · Accepted Answer · 2011-09-12 12:53:22Z

2

Here's a pattern that works:

/^[^\d]+?\d+[^\d]+?\d+[\.]?\d+$/

Note that [^\d]+ means at least one non digit character.

On second thought, here's a more generic solution that doesn't need to deal with regular expressions:

str.gsub(/[^\d.-]+/, " ").split.collect{|d| d.to_f}

Example:

str = "blabla9999 some more text -1.1"

Parsed:

[9999.0, -1.1]

edited Sep 12, 2011 at 12:53

answered Sep 12, 2011 at 12:46

Roland Mai

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Comments

stema · Accepted Answer · 2011-09-12 12:48:38Z

2

The parenthesis have different meanings.

[] defines a character class, that means one character is matched that is part of this class

() is defining a capturing group, the string that is matched by this part in brackets is put into a variable.

You did not define any anchors so your pattern will match your second string

blabla9999 some more text 1.1
      ^^^^  here          ^^^ and here

Maybe this is more what you wanted

^(\s*-?\d+(?:\.\d+)?\s*)+$

See it here on Regexr

^ anchors the pattern to the start of the string and $ to the end.

it allows Whitespace \s before and after the number and an optional fraction part (?:\.\d+)? This kind of pattern will be matched at least once.

edited Sep 12, 2011 at 12:48

answered Sep 12, 2011 at 12:40

stema

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2 Comments

Cedric H. Over a year ago

"You did not define any anchors": what do you mean by anchor ?

stema Over a year ago

@Cedric an anchor anchors the pattern to certain points, like the start of the string or of a word. without it you allow your pattern starting to match directly after your letters.

dfens · Accepted Answer · 2011-09-12 14:02:46Z

2

maybe /(-?\d+(.\d+)?)+/

irb(main):010:0> "910     -6.258000  6.290".scan(/(\-?\d+(\.\d+)?)+/).map{|x| x[0]}
=> ["910", "-6.258000", "6.290"]

answered Sep 12, 2011 at 14:02

dfens

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Comments

Lars Haugseth · Accepted Answer · 2011-09-12 22:25:58Z

0

str = "    910     -6.258000  6.290"
str.scan(/-?\d+\.?\d+/).map(&:to_f)
# => [910.0, -6.258, 6.29]

If you don't want integers to be converted to floats, try this:

str = "    910     -6.258000  6.290"
str.scan(/-?\d+\.?\d+/).map do |ns|
  ns[/\./] ? ns.to_f : ns.to_i
end
# => [910, -6.258, 6.29]

answered Sep 12, 2011 at 22:25

Lars Haugseth

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