I want to get the count of occurrence of a substring within a string.
My string is "hello hello hello". I want to get the number of times "hello hello" occurs in it, which in the above case is 2.
Can someone please help me find a regex for it?
views:
135answers:
6
+1
Q:
Regex for finding number of times substring "hello hello" occurs in string "hello hello hello"
+2
A:
Try:
(?=hello hello)
Using a lookahead lets you find overlapping results. For whole word only, you may try:
\b(?=hello hello\b)
Example: http://rubular.com/r/om1xn1FmBI the blue positions mark a match
Kobi
2010-10-19 05:14:56
+1
A:
Assuming you meant "hello" and not "hello hello" , you can just split on hello. No need to construct extra regex
$string="hello hello blah hello blah helloworld hello blah blah hello";
@s = split "hello", $string, -1;
print scalar @s - 1 ."\n"; #get size of array
ghostdog74
2010-10-19 05:25:24
Now, I'm no perl guy, but isn't `/hello/` a regex? In that case, you might as well match against it. Also, note that the question asks about `"hello hello"`, which suggests overlapping matches.
Kobi
2010-10-19 05:29:16
Note that /hello/ is a regex, though :-)
Thilo
2010-10-19 05:30:01
@Kobi: +1. While split can probably be done without a regex, overlapping would be a problem.
Thilo
2010-10-19 05:32:14
and note that question also says 3. Unless the OP redefines that, whether is overlapping or not is pure guess work
ghostdog74
2010-10-19 05:34:36
That is correct `:)`
Kobi
2010-10-19 05:36:32
+1
A:
This is what you are looking for actually, Counting the occurrences of a substring - the fastest way.
Vantomex
2010-10-19 05:26:10
A:
use strict;
use warning;
my $str = "hello hello hello bla bla hello bla hello";
my $count = grep /hello/ , split /\s+/,$str ;
print"$count"; #output 5
Nikhil Jain
2010-10-19 05:31:33
providing more `general solution` ie., first by splittig the string into words and then check by `grep` whether it is required word or not.
Nikhil Jain
2010-10-19 05:37:42
how is assuming that matching only needs to be done on word boundaries more general? (especially since "hello hello" is not one word)
Thilo
2010-10-19 05:39:32
yes that's true, but i am considering "hello" as one word unless OP explain it more and split string into words because assuming that string may contain words other than "hello".
Nikhil Jain
2010-10-19 05:55:55
+3
A:
Depending on either you want to count the number of occurrence of hello (which is 3 in your example) or hello hello (wich is 2), you can do:
#!/usr/bin/perl
use 5.10.1;
use warnings;
use strict;
my $str = q/hello hello hello/;
my $count1 =()= $str =~ /(?=\bhello hello\b)/g;
say $count1; # gives 2
my $count2 =()= $str =~ /\bhello\b/g;
say $count2; # gives 3
M42
2010-10-19 08:04:44