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Regular Expression Help

Posted on 2016-09-01
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I need a regular expression that will identify  decimal values that are  less 3 digits in length..

For example:

1.0  --> Yes
2.00 --> Yes
0.01 -->  Yes
0.008 --> No
4  --> no
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Question by:tmajor99
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by:TechieMD
ID: 41780518
^[0-9]*(?:\.[0-9]{1,2})?$

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by:Jeff Darling
ID: 41780534
^\d{1,2}\.\d{1,2}$

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by:TechieMD
ID: 41780543
Jeff, the regex you provided wouldn't allow for 111.0 which according to the question should be a valid match. A correction to mine though:
^[0-9]*\.[0-9]{1,2}$

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As 4 should fail but 4.0 shouldn't.
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Expert Comment

by:Jeff Darling
ID: 41780647
The specs say "less 3 digits in length".  so 11.0 or 1.11 would match, but not 111.0 because that is 4 digits.  The question doesn't say, but I'm assuming that there won't be a number without a leading or trailing digit on the decimal.  so 0.01 for example and not just .01

I'm assuming 4 doesn't match because its not a decimal value.
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by:Terry Woods
Terry Woods earned 500 total points (awarded by participants)
ID: 41780734
I'm assuming the following are invalid:
111.
.111
111

This isn't the most efficient pattern to run, but performance is not usually the problem with a regex (it's usually the correctness or edge cases that are a problem):
^(?=\d+\.\d+)(?!(\d.*){4}).*$

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To help you adjust it if you need to:
(?=\d+\.\d+) is a lookahead that requires at least one digit before and after a decimal point
(?!(\d.*){4}) is a negative lookahead that invalidates any values with 4 or more digits
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by:Terry Woods
ID: 41780738
Jeff, your pattern will match 11.11, which I understand is incorrect.
TechieMD, yours will match 111111.1 and also .1, which I understand is incorrect.
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by:TechieMD
TechieMD earned 500 total points (awarded by participants)
ID: 41780799
There is insufficient data from the examples in the question to extrapolate whether the asker wants to see only three digits in total or a maximum of two decimal places.

Waiting for asker clarification.
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Jeff Darling earned 1000 total points (awarded by participants)
ID: 41781490
@Terry

Thanks, I missed that test case.  It wasn't listed.

^\d{1,1}\.\d{1,2}$|^\d{1,2}\.\d{1,1}$

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If the correct spec is Zero leading or  trailing digits, then that would change the pattern.
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