Regular Expression to extract a number from inside a custom string

Question

I'm learning Regular Expressions.

I'm trying to find the best way of writing an expression that extracts a number from within the parenthesis that follows the character R" so:

Example 1:

String("257*5.6+48.9/2*R(64)")

reg ex would return the numeric value inside R() in this case 64.

Example 2:

String("sin(45)*55 + X^2+R(-64.525)")

reg ex would return the numeric value inside R() in this case -64.525

My expression so far is:

/R\(\-?\d+\.?\d+\)/g

which returns R(number) taking into account possible decimal places and negative values.

Is there a better regular expression to match(return) only the number from inside the parenthesis that follows the character R?

Many thanks in advance for advice / help.

D

...extracted from Adobe's website: "ActionScript 3.0 implements regular expressions as defined in the ECMAScript edition 3 language specification (ECMA-262)" — user2190690
– user2190690, Commented Oct 21, 2014 at 8:08

Tim Pietzcker · Accepted Answer · 2014-10-21 07:51:54Z

2

If you're using a regex engine other than JavaScript, you can use positive lookaround assertions:

/(?<=R\()-?\d+\.?\d*(?=\))/g

answered Oct 21, 2014 at 7:51

Tim Pietzcker

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2 Comments

Avinash Raj Over a year ago

i think you made a mistake by putting \.?\d* in your regex instead of (?:\.\d+)? , i'll delete my answer because it's most similar to your's except the one i mentioned.

Tim Pietzcker Over a year ago

@AvinashRaj: You're right, this was just a quick and dirty fix in order not to prevent matches of single-digit integers. But who knows which number formats are valid (.1 and 2. might all be valid, so neither of our regexes might be the ultimate solution)...

Braj · Accepted Answer · 2014-10-21 07:57:43Z

2

Get the matched group from index 1

R\((-?\d+(\.\d+)?)\)

Online demo

Use surrounding parenthesis as well for getting the desired output:

R\(([^\)]*)

Online Demo

Pattern explanation:

  R                        'R'
  \(                       '('
  (                        group and capture to \1:
    [^\)]*                   any character except: '\)' (0 or more times)
  )                        end of \1

Try Positive Look behind that do not consume characters in the string, but only assert whether a match is possible or not if supported by the language:

(?<=R\()[^\)]*

Online demo

edited Oct 21, 2014 at 7:57

answered Oct 21, 2014 at 7:51

Braj

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1 Comment

user2190690 Over a year ago

Hi Braj, in AS3 your second suggestion works (?<=R()[^)]*. For testing RegEx that works in AS3 I've found regexr.com to be more compatible. I don't know enough about RegEx to comment why.

vks · Accepted Answer · 2014-10-21 08:01:59Z

0

R\((\S+?)\)

You can try this.See demo.

http://regex101.com/r/dK1xR4/11

answered Oct 21, 2014 at 8:01

vks

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2 Comments

user2190690 Over a year ago

I couldn't get this to return only the number in AS3 although it clearly works in test sites.

vks Over a year ago

@user2190690 try R((.*?))

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