Parsing doubles from a String

Question

This question is continuation of this question. The problem is that regex "[-+]?\\d*\\.?\\d+([eE][-+]?\\d+)?" doesn't correctly find doubles.

For instance, input sdf9.99e.23 contains no doubles, cause if we have [eE], after it MUST be a [+-] or just [0-9].

So I need some kind of "if" in the regex. In pseudo-code it'll be like this: if(char[i]==(e|E)) then if(char[i+1] == ('+'|'-')) else return null.

So would sdf9.99f.23 contain a double (or two)? I'd argue that sdf9.99e.23 contains two double values: 9.99 and .23. The whole problem of parsing unstructured text is that it's simply far too open to interpretation. Unless you have a very specific definition you can always find a case that could be argued over. — Joachim Sauer
– Joachim Sauer, Commented Mar 1, 2012 at 7:54
@Helgus: but why is e so special that it "breaks" the string. Why doesn't f do the same? Or an empty space? Why do you choose to ignore any other malformed non-number, but that specific case should cause your algorithm to return an error? In 1a you find 1, in 1b you find 1, in 1c you find 1, in 1d you find 1, but in 1e you return an error. Why is that? — Joachim Sauer
– Joachim Sauer, Commented Mar 1, 2012 at 8:38
What about e1e2e3e4e5e Does this have five, three, two or no doubles? — Peter Lawrey
– Peter Lawrey, Commented Mar 1, 2012 at 9:06
This is not an exact definition. Unfortunately for you, your "correctly" (according to comments) diverges with others' ones. Therefore you need to provide exact definition. "string like this 9.99e.23 is wrong" isn't full and exact definition. Sorry, but if I (or others) will not cavil at every word, you'll get inexact/wrong algoritm or will not get at all. — kirilloid
– kirilloid, Commented Mar 2, 2012 at 8:55

kirilloid · Accepted Answer · 2012-03-02 08:50:04Z

0

Using telepathy(anticipation) to extend your algorithm and disallow digits, dot, non-digit as number I may suggest these 3 regex's. Use them consecutively on the same string and unite (concat, append) results.

"[+-]?\\d+((?![\d.])|$)" // ±digits w/o dot after them (actually, this is integer)
"[+-]?\\d+\\.\\d+((?![\deE])|$)" // ±digits, dot, digit w/o [eE] after them
"[+-]?\\d+\\.\\d+[eE][+-]?\\d+" // full variant: ±digits, dot, digits, "e", ±digits

I tried some approach for combining that into one regexp, but unfortunately it doesn't work.

answered Mar 2, 2012 at 8:50

kirilloid

14.4k6 gold badges42 silver badges54 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Parsing doubles from a String

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related