Contributed by vroom
on Jan 18, 2000 at 23:42 UTC
Q&A
> regular expressions
Answer: How do I find the Nth occurrence of a pattern?
contributed by Roy Johnson A recent discussion found this to be the fastest way, and it's pretty slick:
$_='abcabbcabbbbcabcabbcab';
my $n = 3; ## Find the $nth occurrence
my $pat = qr/ab+/; ## of this pattern
my ($NthMatch) = /(?:.*?($pat)){$n}/;
print "Match #$n looks like $NthMatch\n";
The regex is: find the pattern (optionally preceded by something that isn't the pattern) n times. The pattern is in parens, so the final match will be returned. | Answer: How do I find the Nth occurrence of a pattern?
contributed by maverick you could use =~ in array context like:
$string = "12 34 56 78 90 98 76 54 32 10";
(@matches) = ($string =~ /(\d+)/g);
print "fifth match is $matches[4]\n";
print "eigth match is $matches[7]\n";
/\/\averick | Answer: How do I find the Nth occurrence of a pattern?
contributed by eak Here is my monkified version of the nth_iter subroutine. You gotta love map{}.
#!/usr/bin/perl -w
my @string = (34, 56, 78, 90, 98, 76, 54, 32, 10, 12, 13, 16, 19, 20,
+10, 56);
sub nth_iter{
my ($item, $n, $list) = @_;
( map { $string[$_] == $item ? $_ : (); } 0..$#string )[--$n] or -1;
}
print nth_iter(78, 1, \@string);
| Answer: How do I find the Nth occurrence of a pattern?
contributed by vroom Use the /g (global) to find all occurrences in a string. Place the matching statement within a while loop and count until you get to the wanted number.
$n=5; #want the 5th occurrence of a group of 5 numbers
$count=0;
while(/(\d{5})/g){
if(++$count==$n){
print "The $n\th occurrence was $1\n";
}
}
| Answer: How do I find the Nth occurrence of a pattern?
contributed by poolpi With split
my $string = "12 34 56 78 90 98 76 54 32 10";
my $n = 3;
print+ (split( /[^\d+]/, $string))[$n-1];
# output => 56
my $string ='abcabbcabbbbcabcabbcab';
my $n = 3;
print+ (split( /[^(?:ab+)]/, $string ))[$n-1];
# output => abbbb
| Answer: How do I find the Nth occurrence of a pattern?
contributed by Anonymous Monk Here is a way to do this. This is more C than perl. I'd love for a monk to translate it.
This defines a function that takes:
the item to find,
the teration to locate,
an arry to search
This returns the array index of the nth element.
You get a -1 if none found.
@string = qw(34, 56, 78, 90, 98, 76, 54, 32, 10, 12, 13, 16, 19, 20, 1
+0, 56);
sub nth_iter {
my($item, $n, @list) = @_;
$i = -1;
$match = 0;
$len = @list;
while ($i++ < $len) {
if($list[$i] == $item) {
$match++;
if ($match == $n) {
last;
}
}
}
if ($match != $n) {
$i = -1;
}
return $i;
}
print nth_iter(78, 1, @string);
Rock on! -Ty | Answer: How do I find the Nth occurrence of a pattern?
contributed by cLive ;-) Haven't tested this, but liked the idea.... :)
my $n = whatever...
my $i=0;
while ( ($string =~ /PATTERN/g) && ($i < $n ) ) {
$i++;
}
my $NthMatch = $1;
|
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