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up vote 9 down vote favorite
1

This question already has an answer here:

I have a JavaScript array:

var j_array = new Array();
j_arry=["class:1","division:a","class:5","class:3","division:b","division:c","division:d","class:10"];

I need to find how many times the class is coming and its array key, so I use:

found = $.inArray('class', j_array); ` But it returns `-1`;

Then I use:

var search = 'class';
$.each([j_array], function(index, value){
    $.each(value, function(key, cell){
        if (search.indexOf(cell) !== -1)
            console.log('found in array '+index, cell);
    });
});

But that is also wrong. How do I solve this?

From this array I want to get the following:

  1. Class coming 4 times, at key 0, 2, 3, and 7

  2. I want to make a separate array of class only, that is,

    new_array = ["class:1", "class:2", "class:3", "class:10"];

  3. Currently there are four classes in j_array. How can I get the Nth class value

That is, 1st class value ="class:1", 2nd class value="class:5", etc.

share|improve this question

marked as duplicate by Gothdo javascript 5 hours ago

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
5  
No need for jQuery here, use native array methods – Paul S. 13 hours ago
1  
Why do you need the nested loop ? – user2240414 13 hours ago
    
1 . dont use nested loop 2. do reverse e.g item.indexOf(searchTerm); – user2240414 12 hours ago
    
This question is definitely too broad—there are many possible ways to do it. – Gothdo 5 hours ago
up vote 11 down vote

You could filter elements which match in a new array and just return the length of this new array 

var j_arry = ["class:1","division:a","class:5","class:3","division:b","division:c","division:d","class:10"];
var res = j_arry.filter(x => x.includes("class"));
var key = res.map(x => x.split(":")[1]);
console.log("Class coming " + res.length + " , at key " + key.join(","));
console.log("new array = ", res);

share|improve this answer
up vote 7 down vote

Use Array.prototype.filter to filter out the elements of the array that contains the string class - see demo below:

var j_array =["class:1","division:a","class:5","class:3","division:b","division:c","division:d","class:10"];

var result = j_array.filter(function(e){
  return e.indexOf('class')!==-1;
});

console.log(result);

EDIT:

To get the list of indexes too, you can try this:

var j_array =["class:1","division:a","class:5","class:3","division:b","division:c","division:d","class:10"];

var filteredIndices = []

var filtered = j_array.filter(function(e,i){
  if(e.indexOf('class')!==-1) {
    filteredIndices.push(i);
    return true;
  } else {
    return false;
  }
});

console.log(filtered);
console.log(filteredIndices);

// Nth class value
console.log(filtered[2]); // this prints the 3rd one
.as-console-wrapper{top:0;max-height:100%!important;}

share|improve this answer
1  
Thank you friend . But i have 3 question . Could you please answer for this separate 3 question . – Kamal 13 hours ago
    
question (1) and (2) would be clear from the result in the demo above... For (3) you can do result[N]... – kukkuz 13 hours ago
2  
No friend . Actually you give the answer for question 2, and result[N] is based on new array . But i want result[N] based on J_array. And i cannot find answer for 1st question . – Kamal 13 hours ago
    
for (1), you need a array like [0,2,3,7]? – kukkuz 12 hours ago
    
Yes. Please update this in your answer . – Kamal 12 hours ago
up vote 3 down vote

Here is the answer to your questions 1 + 2. It is also 'n' proof so answers your part 3 also. This works by old-fashioned hard graft rather than funky functions. The original array entries are split and filtered then if qualifying we store in an associative array (results) using a pointer array (list) to make it easier to give a sorted result and pull the values from the associative array. The max variable is probably not necessary but included for clarity - could have used list.length instead. Note that the list[] array will be sparse (missing steps) so we test each entry before use in the output steps.

		var j_array = new Array();
		j_arry=["class:1","division:a","class:5","class:3","division:b","division:c","division:d","class:10","class:1"];

		var a, result = [], list=[], max = -1    
		for (var i =0; i < j_arry.length; i = i + 1) {

			var a = j_arry[i].split(":")
		  if ( a[0] === "class") {
		  
				var key = "c" + a[1]
			  if ( !result[key] ) { result[key] = {pos:[]}}
				result[key].cnt = result[key].cnt ? result[key].cnt + 1 : 1; 
					result[key].pos.push(i)
					list[parseInt(a[1])] = "c" + a[1]  
			  
			  max = parseInt(a[1]) > max ? a[1] : max;
		  }
		}

		// say locations
		for (var i = 0; i < max; i = i + 1) {
			if (list[i]) {
			key = "c" + i 
				console.log("Class " + i + " occurs  at " + result[key].pos.toString()  )
		  }
		}

		// make new array
		var newArray=[]
		for (var i = 0; i < max; i = i + 1) {
			if (list[i]) {
				newArray.push("Class:" + i)
		  }
		}
		console.log("New array=" + newArray.toString()  )

Results are:

Class 1 occurs at 0,8 Class 3 occurs at 3 Class 5 occurs at 2 New array=Class:1,Class:3,Class:5

share|improve this answer
up vote 3 down vote

Single reduce is sufficient here.

var arr = ["class:1","division:a","class:5","class:3","division:b","division:c","division:d","class:10"],
    res = arr.reduce((p,c) => c.includes("class") ? (p.count++, p.keys.push(c.split(":")[1]), p)
                                                  : p ,{count:0, keys:[]});
console.log(res);

share|improve this answer
up vote 3 down vote

You can use the filter and map functions to filter your array to have only elements that match the text 'class', and use array index notation to access the nth element in the array. Check the below code snippet I hope it will be of help to you.

The below code snippet uses ES6 arrow syntax.

var arr = ["class:1", "division:a", "class:5", "class:3", "division:b", "division:c", "division:d", "class:10"];
var result = arr.filter(x => x.indexOf('class') !== -1);
var indices = result.map(x => arr.indexOf(x));
console.log(indices);
console.log(result);

var nValue = window.prompt('Enter n value');
console.log(result[nValue]);

share|improve this answer
up vote 3 down vote

If you're using jQuery to support some really old browser that still don't implement the new Array functions, and you don't want to polyfill those because you're already using jQuery, then you can use the jQuery equivalents:

var arr = ["class:1", "division:a", "class:5", "class:3", "division:b", "division:c", "division:d", "class:10"]
var result = $.grep(arr, function (x) { return x.indexOf('class') !== -1 })
var indices = $.map(result, function (x) { return arr.indexOf(x) })

This is the same code as this answer, but using jQuery.

share|improve this answer
up vote 1 down vote

You have to do map first then filter. 

var j_array = ["class:1", "division:a", "class:5", "class:3", "division:b", "division:c", "division:d", "class:10"];

var result = j_array.map(function(e, i) {
  return e.indexOf('class') > -1 ? '' + i : false;
}).filter(function(e) {
  return !!e;
});
console.log(result);

share|improve this answer

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