RegExp: Add a "-" every 3 characters from right to left

[BautistaC888]

Hello,
I need a regular expression that transforms expressions like this:
40304023
Into this:
40-304-023
Thank you.

[marcusblackhill]

So, close to what @mpennington  present, I think you can combine these 2 formulas:

1. Reversestring(regex_replace(ReverseString([Field1]),"(\d{3})","$1-"))
2. IIF(Left([Field1],1)="-", Right([Field1], Length([Field1])-1),[Field1])

Like that:

[mpennington]

@BautistaC888 , 

Definitely along the same line as @marcusblackhill , just a slightly different variation, that is harder to read, but is should handle up to 15 digit numbers:

TrimLeft(
REGEX_Replace(
ReverseString(REGEX_Replace(
ReverseString((ToString([Number],0))),
"(\d{3})(\d{3})?(\d{3})?(\d{3})?(\d{3})?(\d{0,2})?","$1-$2-$3-$4-$5-$6")
),'-{2,}','-'),'-')

[apathetichell · Accepted solution]

There's been a lot of great answers on this thread from @mpennington  and @marcusblackhill 

here's one more example of the magnificent value of regex in replace mode...

(\d{3}) in replace mode

$1- (replacement text)

and a few reverses and a trim...

Or trimleft(reversestring(REGEX_Replace(reversestring(tostring([Field1])), "(\d{3})", "$1-")),"-") for the one tool formula.

[mpennington]

@apathetichell I really like your method, as it works regardless of the length. Great stuff!

[apathetichell]

Thanks! I love learning from all of these different approaches on these discussions!

[RaviP]

Really like @apathetichell 's solution. It is more generic.

If it is specifically 3 characters, we could may be just use a thousand separator?

replace(tostring([Field],0,1),',','-')

Ravi