Count number of elements in an array using Javascript

Question

I have an assignment for a Javascript course where I have to count how many of each specific types of elements occur in an array. The array is 105 elements long, and just occurrences of the numbers 1, 2, 3, 4, and 5. I have to count how many 1's, 2's, 3's, etc.

Of course there's a simple way to do this using a loop however my teacher has added the following at the end of the assignment:

Use only the length property, toString(), sort() and indexOf() methods. Please no loops or conditional statements.

I have no idea how to do this assignment without using a loop. Any help you can give me is greatly appreciated. Thanks!

After sorting the array, look at the indexes of first occurrences of digits. — halfbit
– halfbit, Commented Sep 29, 2013 at 13:45
ok then what do I do? array sorted. how do I fetch the total count without a loop or statement? — user2513846
– user2513846, Commented Feb 10, 2015 at 4:40

Gaurav Singla · Accepted Answer · 2013-09-29 13:49:08Z

2

this will be the answere:

var c=[1,2,3,4,5,2,3,4,5]
    c.sort()

    cout_of_1 = c.indexOf(2)-c.indexOf(1);
    cout_of_2 = c.indexOf(3)-c.indexOf(2);
    cout_of_3 = c.indexOf(4)-c.indexOf(3);
    cout_of_4 = c.indexOf(5)-c.indexOf(4);
    cout_of_5 = c.length-c.indexOf(5)+1;

answered Sep 29, 2013 at 13:49

Gaurav Singla

1,4611 gold badge18 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Bill the Lizard · Accepted Answer · 2013-09-29 13:49:17Z

1

Since this is an assignment and you haven't really shown an attempt, I'll just give you a couple of hints.

Once you sort the array, all of the 1s will be grouped together at the start of the array, then all the 2s, etc.
The indexOf function returns the first index at which a given element can be found in the array, or -1 if it is not present.

Given the index of the first occurrence of each digit in a sorted array, you should be able to calculate how many of each digit there are. I'm not sure you'll need toString() at all. Your instructor might have thrown that in to be sneaky.

answered Sep 29, 2013 at 13:49

Bill the Lizard

407k213 gold badges579 silver badges892 bronze badges

1 Comment

user2513846 Over a year ago

I still dont understand how to get the total count of a number after I sorted the array. totally lost. all the solutions around are with loops or statements. Isn't this suppose to be as easy as introductory course exercises so you can understand as array? No wonder why you get discouraged so easily.

Broxzier · Accepted Answer · 2013-09-29 13:53:47Z

0

First, sort the array, then grab the first occurrence of the next value. That's the amount of numbers you have, minus the ones you already have.

var array = [1,2,5,3,2,4,5,2,1,3,3,4,5,6,2];
array = array.sort();

var ones = array.indexOf(2);
var twos = array.indexOf(3) - ones;
var threes = array.indexOf(4) - ones - twos;
...

However for the last value (5) there is no next value to check. You can work around this by checking the length and subtracting one from it.

var fives = array.length - ones - twos - threes - fours;

Keep in mind that this is actually bad code, and you should use loops.

answered Sep 29, 2013 at 13:53

Broxzier

2,95920 silver badges37 bronze badges

Collectives™ on Stack Overflow

Count number of elements in an array using Javascript

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related