Get the Index of the Nth Occurrence of a String

Get the index of the nth occurrence in a string

You can use split, slice & join to achieve your requirement.

Logic

First split your string with char then use slice to join split values upto nth occurrence. Then simply join with char. It's length will be your answer.

Check below.

function getIndex(str, char, n) {  return str.split(char).slice(0, n).join(char).length;}
console.log(getIndex('https://www.example.example2.co.uk', '.', 2)) // returns 19console.log(getIndex('https://www.example.example2.co.uk', '.', 1)) // returns 11console.log(getIndex('https://www.example.example2.co.uk', '.', 3)) // returns 28

Get the index of the nth occurrence of a string?

That's basically what you need to do - or at least, it's the easiest solution. All you'd be "wasting" is the cost of n method invocations - you won't actually be checking any case twice, if you think about it. (IndexOf will return as soon as it finds the match, and you'll keep going from where it left off.)

Find the nth occurrence of substring in a string

Mark's iterative approach would be the usual way, I think.

Here's an alternative with string-splitting, which can often be useful for finding-related processes:

def findnth(haystack, needle, n):
    parts= haystack.split(needle, n+1)
    if len(parts)<=n+1:
        return -1
    return len(haystack)-len(parts[-1])-len(needle)

And here's a quick (and somewhat dirty, in that you have to choose some chaff that can't match the needle) one-liner:

'foo bar bar bar'.replace('bar', 'XXX', 1).find('bar')

How to get the nth occurrence in a string?

const string = "XYZ 123 ABC 456 ABC 789 ABC";
function getPosition(string, subString, index) {  return string.split(subString, index).join(subString).length;}
console.log(  getPosition(string, 'ABC', 2) // --> 16)

Get index of nth occurrence of char in a string

Using LINQ to find the index of the 5'th a in the string aababaababa:

var str = "aababaababa";
var ch = 'a';
var n = 5;
var result = str
  .Select((c, i) => new { c, i })
  .Where(x => x.c == ch)
  .Skip(n - 1)
  .FirstOrDefault();
return result != null ? result.i : -1;

How to get the nth occurrence of a set of substrings in a given string using Javascript?

You could try using Regular Expressions like this:

let testString="A <br> B <br/> C <br /> D <br/>";

//Array of substrings to be searched for
let testItems=['<br>','<br/>','<br />']; 

//Construction of the regular expression from the given array
let regex=new RegExp(testItems.join("|"),"g"); 

//Getting all matches for the provided regex and reducing it to an array of indices only
let indices=[...testString.matchAll(regex)].map(match=>match.index);

console.log(indices);

In a string, how to find the index of the first character of the nth occurrence of a substring Python

Here's a pretty short way:

def index_of_nth_occurrence(longstring, substring, n):
    return len(substring.join(longstring.split(substring)[:n]))
    

longstring = "stackoverflow_is_stackoverflow_not_stackoverflow_even_though_stackoverflow"
substring = "stackoverflow"
n = 2

print(index_of_nth_occurrence(longstring, substring, n)
# 17

The trick here is using str.split() to find non-overlapping occurrences of the substring, then join back the first n of them, and check how many characters that totals up to. The very next character after would be the first character of the nth occurrence of the substring.

This may be less efficient than an iterative/manual approach, and will ignore overlapping matches, but it's quick and easy.

Index of nth Occurrence of the string

There is a find_nth template function in Boost: http://www.boost.org/doc/libs/1_54_0/doc/html/boost/algorithm/find_nth.html

#include <iostream>
#include <boost/algorithm/string/find.hpp>

using namespace std;
using namespace boost;

int main() {

    string a = "The rain in Spain falls mainly on the plain";

    iterator_range<string::iterator> r = find_nth(a, "ain", 2);
    cout << std::distance(a.begin(), r.begin()) << endl;

    return 0;
}