Question

Is there a way to write a regular expression pattern that will create one or two groups based on the input text. (i.e.)

// ONE
NSString *pattern = @""; ([0-9]+).([0-9]+)
NSString *inputText = @"ThisIs MyTest72.56String";
// OUTPUT match = 72.56, group1 = 72, group2 = 56

What I am trying to get is:

// TWO
NSString *pattern = @""; ([0-9]+).([0-9]+)
NSString *inputText = @"ThisIs MyTest72String";
// OUTPUT match = 72, group1 = 72, group2 = Empty

I was thinking I could use (?:) but that just removes the group

What I am after is:

Text = "ThisIs MyTest72String"
Match = 72
Group1 = 72
Group2 = Empty

Text = "ThisIs MyTest72.56String"
Match = 72.56
Group1 = 72
Group2 = 56

EDIT:

This sort of works, although I would like to get rid of the “S” in the initial match.

Pattern = ([0-9]+).([0-9]*)
Text = "ThisIs MyTest72String"
Match = 72S
Group1 = 72    //RangeAtIndex:1 {13,2}
Group2 = Empty //RangeAtIndex:2 {16,0}

Text = "ThisIs MyTest72.56String"
Match = 72.56
Group1 = 72
Group2 = 56

This is close, but in the case of “Empty” (Group2) I was expecting the rangeAtIndex:2 to equal NSNotFound. The docs say “The range {NSNotFound, 0} is returned if one of the capture groups did not participate in this particular match” does the group being empty not count as “Not participating”?

Answer 1

Does this give you what you want?

([0-9]+)(?:\.([0-9]+))?

I’ve escaped the decimal place (which you hadn’t, unsure if this is needed in your target language) and grouped the decimal and everything after it as a optional non captured group.

Should just be a matter of checking for the existence of a second group.