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up vote 2 down vote favorite

I have an array:

var locations = ['Afghanistan','Albania','Algeria','New York'];

and a string:

var string = 'I love Afghanistan New York Afghanistan Andorra Andorra Algeria New York';

I want to count the number of times each keyword in the array appears in the string but can't figure out the best way to do that.

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4 Answers 4

up vote 5 down vote accepted

Here is my version:

function countItems(a, s) {
    var x, i, output = {};
    for (x = 0; x < a.length; x++) {
    	i = 0;
    	output[a[x]] = 0;
    	while ((i = s.indexOf(a[x], i)) > -1) {
    		output[a[x]]++;
    		i++
    	}
    }
    return output;
}

var result = countItems(locations, string);
// result['Albania'] === 0

Try it out here.

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Suggestion: Do a reverse while-loop. That should speed things up a bit, when dealing with a large string and/or a large array. –  roosteronacid Sep 9 '09 at 17:12
    
this works great. The only thing I changed was that I hate how JS does associative arrays so instead I return a multi-dimensional array: output[keyword,count] –  STHayden Sep 9 '09 at 18:24
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up vote 4 down vote

Try something like this. You could modify what you do with count -- store it in another array, display it (which is what this script does), etc.

var locations = ['Afghanistan','Albania','Algeria','New York'];
var str = 'I love Afghanistan New York Afghanistan Andorra Andorra Algeria New York';


for(var i=0; i<locations.length; i++) {
    var pattern = new RegExp(locations[i], "g");
    var m = str.match(pattern);
    if (m != null)
    {
       var count = m.length; // the count
       alert("There are " + count + " occurrences of " + locations[i]);
    }
}
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up vote 1 down vote 
<script language="JavaScript">
var locations = ['Afghanistan','Albania','Algeria','New York'];

var string1 = 'I love Afghanistan New York Afghanistan Andorra Andorra Algeria New York';

for (var i=0;i<locations.length;i++) {
  nCount = string1.split(locations[i]).length-1;
  document.write(locations[i] + ' is found ' + nCount + ' times<br>');
}

</script>
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Ingenious to use the pattern as a delimiter... A bit overkill, though, regarding you throw away the array. –  xtofl Sep 9 '09 at 17:13
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up vote 1 down vote

This code only instantiates one RegExp object and uses a reverse while-loop. I'm pretty sure this is as fast as you can go without breaking the laws of physics :)

This is whats happening:

  1. Construct regular expression string using a reverse while-loop
  2. New up just one RegExp object, and match() it on the string
  3. Count the length of the array returned by the match() function

Here's the implementation:

var countries = ["Afganistan", "America", "Island"];
var sentence = "I love Afganistan, America.. And I love America some more";

function countOccurrences(a, s)
{
    var re = "",
        l = a.length,
        m;

    while (l)
    {
        l--;

        re += a[l];

        if (l > 0) re += "|";
    }

    m = s.match(new RegExp(re, "gi")) || [];

    return m.length;
}

Note: I am of course expecting the entries in the array to be sanitized for any special characters that will break the regular expression constructed within the function.

var occurrences = function countOccurrences(countries, sentence); // returns 3
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this seems like a good solution but not to my problem. I want to know the count for EACH keyword. not for all together. thanks though! –  STHayden Sep 9 '09 at 17:48
    
Ah! Misunderstood your question. Thanks for the compliment though :) –  roosteronacid Sep 9 '09 at 18:36
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