Thanks for all the interesting replies to this query. I used
"offset" rather than (what most replies suggested) "repeat" with (or
for) each character thinking it would be faster, but that seems to be
true only if the string is extremely long and the sought for
character very far from the front. And I tried to match the first
"(" rather than building a list of all matches. There is no
practical need for yet another approach, but in case others will find
it of interest here is a speedy one that does not step through each
character and barely uses offset.
David Epstein
function offsetPair a,b,str -- NOTE: a and b are single characters,
str cannot be more than one line
-- in string str, locate the first a, and the nth b, where n = the
number of a's that precede that b
-- e.g., if a = "(" and b = ")" the character positions of the first
matched pair will be returned
-- return 0 if a is not found and empty if no match is found
put offset(a,str) into ca
if ca = 0 then return 0
put numToChar(7) into char 1 to ca of str -- some char that's not
a or b
replace a with return in str
put 1 into na -- number (ordinal) of a's, also the line count in str
put 0 into nb
repeat for each line k in str
if k is not empty then -- does this line have (na-nb) instances
of b?
get nthHit(na-nb,b,k,z,numToChar(7))
if it is not empty then return ca && it+ca+length(line 1 to
na-1 of str)
add z to nb
end if
add 1 to na
end repeat
return empty
end offsetPair
function nthHit n,a,str,@z
-- returns character number of the nth instance of a (a single
character) in str
-- z reports the total number of hits
put numToChar(7) & str & numToChar(7) into str -- so str does
not begin or end with a
set itemDelimiter to a
put -1 + the number of items in str into z
if n > z then return empty
return length(item 1 to n of str)
end nthHit
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