How do I evaluate only the digits after a decimal in a number?

Question

I am using ExamDiff to compare two *.csv files which have no spaces after commas. Numbers in the files contain between 2 and 8 decimal places but I only want to evaluate the first 3 digits after the decimal - anything beyond the thousandth place is insignificant.
ExamDiff allows you to use Regex to ignore certain parts of lines so I'm using: (\d{1,4}\.) to identify the number string (but also ignore it which is Ok in these cases).
Here's a sample line from the csv:

VQ000009,B2,B3,VV,12.0000,0.23,1.0000,1.0000000000,1357.421

And here's the comparable line in the new CSV:

VQ000009,B2,B3,VV,12.0000,0.27,1.0009,1.0000000000,1357.431

So, in this example the 0.23 and 0.27 would flag the 1.0000 and 1.0009 would not flag, and the 1357.421 and 1357.431 would flag

Answer 1

The web site isn't clear as to how much of the Boost library is supported, but if full PCRE is supported, you can use this to ignore:

(?<=\.\d{3})\d+

This says match any digits that are preceded by a . and 3 digits. Note that if you have something like VQ.123456 the 456 will match and be ignored. Stray . will cause issues.