Regex repeated pattern

Question

I am tryting the match the following pattern:

((1.0 4) (2.0 5) .... (10.0 8))

The tuple (X N), where X is a floating point number with optional exponent and N is an integer, can be repeated several times.

I tried on this website and I could generate a regex for a fixed number of tuples. For example for 2 tuples I would get

^\(\(([+-]?(?=\.\d|\d)(?:\d+)?(?:\.?\d*))(?:[eE]([+-]?\d+))?\s[0-9]+\)\s\(([+-]?(?=\.\d|\d)(?:\d+)?(?:\.?\d*))(?:[eE]([+-]?\d+))?\s[0-9]+\)\)$

How can I modify the pattern so that the number of tuples is arbitrary? I think I will have to use some kind of grouping, but regex is quite new for me.

You question needs greater specificity. At first (based largely on your example) I assumed that X is the string representation of a non-negative float with one digit to the right of the decimal point and N was the optional exponent. Now that I look at the regex you give I see neither of those assumptions were correct. At minimum you need to expand your example to include negative floats, exponents and so on. Also, make it a valid Javascript object (in part, no '....') so that readers can test code against your example and variants therefore, including invalid strings. — Cary Swoveland
– Cary Swoveland, Commented Feb 15, 2022 at 19:40

Tim Biegeleisen · Accepted Answer · 2022-02-15 08:10:00Z

3

You may use the following pattern:

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

Demo

This pattern matches:

^
\(                             (
\(\d+(?:\.\d+)? \d+\)          a leading tuple
(?:\s*\(\d+(?:\.\d+)? \d+\))*  space, more tuples
\)                             )
$

edited Feb 15, 2022 at 8:10

answered Feb 15, 2022 at 7:57

Tim Biegeleisen

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2 Comments

Rojj Over a year ago

Wow, that was fast! Almost there. The second number must bit an integer. Your regex also matches ((1.0 2) (2.0 4) (3.0 8.0))

Tim Biegeleisen Over a year ago

It wasn't clear that the second number in the tuple were always an integer. I have updated my answer.

JvdV · Accepted Answer · 2022-02-15 08:18:49Z

"The tuple (X N), where X is a floating point number with optional exponent and N is an integer, can be repeated several times."

To make sure you have 1+ tuples (with optional exponents), you can use:

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

See an online demo

^ - Start-line anchor;
\(\( - Two literal opening paranthesis;
[-+]?\d*\.\d+([eE][-+]?\d+)? - To match your floating point number with optional exponent we match: An optional hypen or plus sign followed by 0+ digits and a literal dot with 1+ digits. After that is an optional capture group to match the exponent with a letter 'e', an optional hyphen or plus and 1+ digits;
\s\d+\) - To finish the tuple the pattern matches: A single whitespace character and 1+ digits to match the integer part of the tuple before a closing paranthesis;
(?:\s.....)* - The trick in the following is that we use a non-capture group to match a single whitespace char and the pattern we used for our tuple. When closing this non-capture group match it 0+ times to allow for any number of tuples;
\)$ - Finish the pattern with a literal closing paranthesis and the end-line anchor.

Or if available, catch the 1st tuple in a capture group and repeat that exact pattern with a backreference:

^\((\([-+]?\d*\.\d+([eE][-+]?\d+)?\h\d+\))(?:\h(?1))*\)$

See an online demo

Cary Swoveland · Accepted Answer · 2022-02-15 09:50:27Z

You can verify the pattern by matching the string with the following regular expression.

^\((?:\(\d+\.\d(?: \d+)?\)(?: |(?=\)$)))+\)$

Demo

The regular expression can be broken down as follows.

^            # match beginning of string
\(           # match '('
(?:          # begin non-capture group
  \(         # match '('
  \d+\.\d    # match 1+ digits, '.', 1 digit
  (?: \d+)?  # optionally ('?') match a space then 1+ digits 
  \(         # match ')'
  (?:        # begin non-capture group
    [ ]      # match a space
    |        # or
    (?=\)$)  # positive lookahead asserts next char is ')' at end of string
  )          # end non-capture group
)+           # end non-capture group and execute one or more times
\)           # match ')'
$            # match end of string

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