JavaScript loop through to check duplicate value

Question

I am having troubles trying to check if the date exists in the array.

 for(var i = 0; i< crisislist.length; i++){
        hazecounter = 1;
        if(crisislist[i].category == 1){
            if(crisislist[i].date != crisislist[i+1].date) {
                hazelabel.push(crisislist[i].date);
            }else{
                hazecounter++; 
            }
            hazedata.push(hazecounter);
        }
 }

The sample data for the date is:

["01-02-2017", "22-03-2017", "22-03-2017", "07-08-2017"]

And the expected output for hazelabel, hazedata should be:

hazelabel: ["01-02-2017", "22-03-2017", "07-08-2017"] hazedata: [1,2,1]

With the code above, when I check until the last element in the array and trying to make a comparison, it throw me an error message:

Uncaught TypeError: Cannot read property 'date' of undefined

I think this is because when I reach the last element of array, and I try to find crisislist[I+1].date, it could not found and thus the error message.

Any idea how to fix this? Thanks in advance!

Can't you just check if `crisislist[i] + 1` is not `undefined` before accessing the `date` property? — Teemoh, Apr 01 '17 at 17:54
you can write it simply like this http://stackoverflow.com/questions/40418507/javascript-filter-array-with-duplicate-dates. jsfiddle demo https://jsfiddle.net/u6u80zsa/ — Sankara, Apr 01 '17 at 18:17

Vivek Doshi · Answer 1 · 2017-04-01T18:01:37.643

0

You just need to check till second last :

for(var i = 0; i< (crisislist.length-1); i++){
        hazecounter = 1;
        if(crisislist[i].category == 1){
            if(crisislist[i].date != crisislist[i+1].date) {
                hazelabel.push(crisislist[i].date);
                if (crisislist.length-2 == i)
                {
                    hazelabel.push(crisislist[i+1].date);
                }
            }else{
                hazecounter++; 
            }
            hazedata.push(hazecounter);
        }
 }

edited Apr 01 '17 at 18:01

answered Apr 01 '17 at 17:54

Vivek Doshi

56,649
12
110
122

But that would ignore the last one? – Bergi Apr 01 '17 at 17:55
just try out it will be compared with second last so it will not – Vivek Doshi Apr 01 '17 at 17:57
compared, yes, but the last item is not looked at separately. – Bergi Apr 01 '17 at 17:59

score 0 · Answer 2 · answered Apr 01 '17 at 17:56

Your if statement is going to be a problem.

if(crisislist[i].date != crisislist[i+1].date) {

You are accessing crisislist[i+1] in a loop that goes to < crisislist.length. That means that if you have an array of size 4, your loop will go until i = 3, but you are accessing i+1 from the array (crisislist[4]), which will be undefined.

Try changing your for loop to go to crisis.length-1

Bergi · Accepted Answer · 2017-04-01T18:00:11.113

You must access crisislist[i+1].date only when i doesn't point to the last element.

Also notice that to get the desired result, you need to move the hazedata.push inside the if block and put the initialisation of hazecounter in front of the loop.

var hazecounter = 1;
for (var i = 0; i< crisislist.length; i++) {
    if (crisislist[i].category == 1) {
        if (i == crisislist.length-1 || crisislist[i].date != crisislist[i+1].date) {
            hazelabel.push(crisislist[i].date);
            hazedata.push(hazecounter);
            hazeCounter = 1;
        } else {
            hazecounter++; 
        }
    }
}

Thanks it works! I was thinking how to check for the last element. — , Apr 01 '17 at 17:58

score 0 · Answer 4 · answered Apr 01 '17 at 18:11

Check that code. If you have any questions, add a comment :) In my solution dates dont have to be sorted.

  </head>

<BODY>
<script>

function Something(date)
{
    this.date = date;
    this.category = 1;
}

var crisislist = [];
var hazelabel = [];
var hazedata = [];
crisislist[0] = new Something("01-02-2017");
crisislist[1] = new Something("22-03-2017");
crisislist[2] = new Something("22-03-2017");
crisislist[3] = new Something("07-08-2017");




 for(var i = 0; i< crisislist.length; i++){
    if(crisislist[i].category == 1)
    {
     if(!hazelabel[crisislist[i].date])
     {
         hazelabel[crisislist[i].date] = crisislist[i].date;
         hazedata[crisislist[i].date] = 1;
     }
     else
     {
         hazedata[crisislist[i].date]++;
     }
    }
 }

for(var key  in hazelabel)
{
console.log(hazelabel[key]);
console.log(hazedata[key]);  
}

</script>
</BODY>
</HTML>

JavaScript loop through to check duplicate value

4 Answers4