Hi All,

Sorry if I'm in the wrong place but I have a question about regular expressions. I'm new to this and am finding them a bit puzzling.

My question is....Some sequences of inputs produce the same sequences as outputs. eg input sequence <0,0,0> produces output sequence <0,0,0>.

What would be the regular expression that describes all such sequences. Is it 0* or 0+ (plus is superscript) ie. is it one or more 0's or zero or more 0's.

Thanks in advance.

Jonno


I rather suspect that you're looking for something like
       <(0,)*0>
which means
* A less that sign
* 0 followe by a comma 0 or more times
* a 0
* a greater than sign

Although a regular expression is a "fuzzy match", you have to be exact in how you descibe that match - you have to know exactly what combinations are allowed and which aren't.  I have made the following assumptions in my answer
* That you're looking for the string embedded anywhere in a piece of text
* That the < and > sign must be present
* That you must have at least one zero present
* That there's no maximum to the number of zeros
* That the , is always present as a separator
* That a trailing , is not allowed
* That white spaces are not allowed anywhere in the sequence.

If any of these assumptions is incorrect, the regular expression will need changing - and there must be hundreds of combinantions of answers to the things I assumed - not only things like "yes" and "no", but "no - white spaces are allowed but only after the comma".  This world of detailed study of what look like simple strings is typical of the regular expression world.

There's a further complexity.  Rgeular expressions differ slightly from one language to another; the common sequences work more or less across the board these days, but the extensions can be different.   Am I allowed a "+" for 1 or more characters?  Is white space a \s, a [ \r\t\n] or a [[:space:]] or a \p{space}, or are several of these allowed?   And so on ...

I hope this answer helps - please do follow up if you want me to tune my answer to meet a different scenario to the one I have assumed (after all - an assumption makes an "ass out of u and me".  If you can tell me what language you would like me to use in my answer, that would be a great help too.

Graham

Thanks for that Graham. The less than and more than symbols are meant to denote the fact that this is an input sequence of a series of zero's. Thats why I thought 0+ (plus sign in superscript). This denotes (I think) a sequence of one or more zero's

Thanks for your help. Its a minefield innit  

Regards Jonno

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