how to extract a number from a string if I know when its starting and when its finishing

Question

for example:

I have the following string

"somestringthatcanbeanything theStringBeforeTheNumber20.47theStringAfterTheNumber somestringthatcanbeanything"

so the number is always between

theStringBeforeTheNumber{number}theStringAfterTheNumber

What I want is to extract the number from the whole string, how can I do that? im using scala how should my regex look like? val myRgx: Regex = """myRegexGoesHere""".r

What language or tool are you using? – Tim Biegeleisen Jun 04 '17 at 10:59 — Tim Biegeleisen, Jun 04 '17 at 10:59
@TimBiegeleisen im using scala – jack miao Jun 04 '17 at 11:00 — jack miao, Jun 04 '17 at 11:00

score 1 · Accepted Answer · answered Jun 04 '17 at 10:59

You can use your suggested pattern, slightly modified as:

val string = "theStringBeforeTheNumber20.47theStringAfterTheNumber"
val pattern = """theStringBeforeTheNumber(.*?)theStringAfterTheNumber""".r
pattern.findAllIn(string).matchData foreach {
    m => println(m.group(1))
}

The quantity in parentheses (.*?) is a capture group and it uses a lazy dot. This says to match everything between the first string and the first occurrence of the second string. We print out the first capture group in the code snippet.

Luis Carlos · Answer 2 · 2017-06-04T11:50:33.457

1

If you know the starting and finish string, I think that is better do a substring() because in general the regexp is costly. For example substring(indexOf(theStringBeforeTheNumber) + length(theStringBeforeTheNumber) , indexOf(theStringAfterTheNumber)) Also you must consider if the initial and final string are equals because the indexes, in that case you have do some extra calculation. Hope this help.

edited Jun 04 '17 at 11:50

answered Jun 04 '17 at 11:06

Luis Carlos

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score 1 · Answer 3 · answered Jun 04 '17 at 16:55

Here's another approach using Regex along with verifying the extracted number:

import scala.util.Try

val s = "somestringthatcanbeanything theStringBeforeTheNumber20.47theStringAfterTheNumber somestringthatcanbeanything"

val pattern = """.*?theStringBeforeTheNumber([0-9.-]*)theStringAfterTheNumber.*""".r

val number: Double = s match {
  case pattern(num) => Try(num.toDouble).getOrElse(-999)
  case _ => -999
}
number: Double = 20.47

how to extract a number from a string if I know when its starting and when its finishing

3 Answers3