calculate the occurence and store the result in a key value-pair using javascript

Question

I need to calculate the occurence of the name in an array.

var eachAuthorData = ["bob","joke","hello","stack","stack","ok","joke","bob"];

I can do this by using a for loop,and get a result like this

{bob: 2, joke: 2, hello: 1, stack: 2, ok: 1}

but the result can only be access using

counts["bob"]

not only do I need to know the occrence of each name. but also need to know how many diffent name in the array eachAuthorData how do I locate bob in the eachAuthorData I only need to use the name once

Answer 1

If you start with an array:

var eachAuthorData = ["bob","joke","hello","stack","stack","ok","joke","bob"];

and you want to know how many of each name there is in the array and how many unique strings there are, you can do it like this:

var counts = {}, i, item, uniques = 0;
for (i = 0; i < eachAuthorData.length; i++) {
    item = eachAuthorData[i];
    if (!counts.hasOwnProperty(item)) {
        counts[item] = 1;
        ++uniques;
    } else {
        ++counts[item];
    }
}

This will generate an output in counts like this:

{bob: 2, joke: 2, hello: 1, stack: 2, ok: 1}

And, since you asked a few other questions in comments, I added the variable uniques which gives you the total unique string count.

And, you would access any individual count like this:

var cnt = counts["bob"];

Or, if the desired key is in a variable named key , you would use:

var cnt = counts[key];

---

If you want to iterate all the counts of all the unique strings, you can do that like this:

for (var item in counts) {
    // item is the key
    // counts[item] is the count
    console.log("counts[" + item + "] = " + counts[item]);
}

Working demo: http://jsfiddle.net/jfriend00/eJyAg/

---

If you want a list of the keys in the counts object (eg the unique strings), you can use:

var keys = Object.keys(counts);

Object.keys() requires IE9 or greater or there's a polyfill here if you want interoperability with older versions of IE.

Answer 2

I think you should have:

var eachAuthorData = ["bob","joke","hello","stack","stack","ok","joke","bob"];

do this to count:

var toMatch, i, count;

toMatch = "bob";
count   = 0;

for( i=0 ; i<eachAuthorData.length ; ++i ){
  if( eachAuthorData[i] == toMatch ){
    ++count;
  }
}

console.log("The element "+ toMatch +" is counted "+ count +" times!");

Answer 3

Try this one

var tempObject = new Object();
function count() {
    array_elements = ["bob","joke","hello","stack","stack","ok","joke","bob"];

    array_elements.sort();

    var current = null;
    var cnt = 0;
    for (var i = 0; i < array_elements.length; i++) {
        if (array_elements[i] != current) {
            if (cnt > 0) {
                tempObject[current]=cnt;
                console.log(current + ' comes --> ' + cnt + ' times<br>');
            }
            current = array_elements[i];
            cnt = 1;
        } else {
            cnt++;
        }
    }
    if (cnt > 0) {
        console.log(current + ' comes --> ' + cnt + ' times');
       tempObject[current]=cnt;
    }

}

count();
console.log(JSON.stringify(tempObject));

Answer 4

Presumably you meant an array like:

var data = ["bob","joke","hello","stack","stack","ok","joke","bob"];

Since others have gone the obvious route, I'll post something a little more robust that accounts for the possibility that the data array has elided members (ie is sparse):

function countMembers(dataArray) {

  for (var i=0, iLen=dataArray.length, o={}, item; i<iLen; i++) {
    item = dataArray[i];

    if (dataArray.hasOwnProperty(i)) {
       if (o.hasOwnProperty(item)) {
          ++o[item];
       } else {
          o[item] = 1;
       }
    } 
  }
  return o;
}

Given:

["bob","joke",,,,"hello","stack","stack","ok","joke","bob"];

others will include a member undefined: 3 , but the above wont.