Dart Regexp replace all but numbers and allow once . or ,

Question

I need to replace everything that is not a number and allow only the first , or ..

final string = _lengthController.text?.replaceAll(RegExp('[^0-9,.]'), '')

This is what I got so far and its working fine but will allow , . more than once.

So how can I replace every , and . after the first one, not one of each but only one in total is allowed.

Solution

You can use

text.replaceAllMapped(RegExp(r'^([^,.]*[.,])|\D+'), (Match m) => 
   m[1] != null ? m[1].replaceAll(RegExp(r'[^0-9,.]+'), '') : '')

The ^([^.,]*[.,])|\D+ regex matches

• ^([^,.]*[.,]) - start of string and then any chars other than , and . and then a . or , captured into Group 1
• | - or
• \D+ - any one or more non-digit chars.

If the first alternative matches, the , and . should be preserved, so .replaceAll(RegExp(r'[^0-9,.]+'), '') is used to remove all chars other than digits, . and ,.

If \D+ matches, it means the first . or , has already been matched, so the replacement for this alternative is an empty string.

Comments

[Wiktor Stribiżew]

I understand r'(?<=\..*)\.|[^0-9,.]+' won't work, right?

[Steven Dz]

no its not working

[Steven Dz]

Thanks for the fast answer, its working fine for the . but not working at all for the ,

[Wiktor Stribiżew]

@StevenDz Can you please provide an example?

[Wiktor Stribiżew]

@StevenDz And what do you expect? 32,,43 is correctly (because you asked to "replace every , and . after the first one, not one of each but only one in total is allowed") converted to 32,43. 321,32 must stay the same.

[Steven Dz]

for me its not converted (Flutter1.26.0-12.0.pre, Dart 2.12.0 )

[Wiktor Stribiżew]

@StevenDz Are you sure you are using my code? You must use raw string literals, r'...', when defining the regex patterns.

[Wiktor Stribiżew]

@StevenDz Ok, at any rate, my code works fine. There is something in yours that interferes with the replacing.

[Steven Dz]

Sorry its working fine, there was another expeption thrown because its not a double with , and so the ui didnt updated. So I need to replace the , with . Thank you