replacing text in a chemical formula string

Question

I'm having trouble writing a function that will take a chemical formula string such as "NiNFe(AsO2)2" and remove one of the elements.
my current attempt is:

pattern = new RegExp(symbol, "g")
formula.replace(pattern, "")

If the symbol is "N" and the formula is "NiNFe(AsO2)2" I end up with "iFe(AsO2)2" instead of the desired "NiFe(AsO2)2". Does anyone know how to code this in such a way that it would distinguish the N from the Ni and replace just that?

Use a negative lookahead to check that you don't have a lowercase letter after: `(?![a-z])`. See http://www.regular-expressions.info/lookaround.html — Casimir et Hippolyte, Apr 09 '14 at 23:17

score 2 · Accepted Answer · answered Apr 09 '14 at 23:26

2

RegExp(symbol+'(?![a-z])','g'); will match the symbol if it is not followed by a lower case letter

answered Apr 09 '14 at 23:26

kennebec

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score 1 · Answer 2 · answered Apr 09 '14 at 23:37

1

Use a negative lookahead. The following will also remove any quantifier it may have:

pattern = new RegExp(symbol + "(?![a-z])" + "\d*", "g");

answered Apr 09 '14 at 23:37

Niet the Dark Absol

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score 0 · Answer 3 · answered Apr 09 '14 at 23:42

0

If for some reason you want to avoid using negative lookahead (eg. javascript supports it but some other regex engines don't), you could simply match symbol + "([^a-z])" and replace with $1.

answered Apr 09 '14 at 23:42

CAustin

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replacing text in a chemical formula string

3 Answers3