loop in dynamically updated array not working

Question

Here is a simple javascript code that adds unique data from one array to another.

var data = [1, 2, 3, 2]
var dump = [];
for (var i = 0; i < data.length; i++) {
    if (dump.length == 0) {
        dump.push(data[i])
    } else {
        for (var a = 0; a < dump.length; a++) {
            if (dump[a] != data[i]) {
                if (a >= dump.length) {
                    dump.push(data[i])
                }
            }
        }
    }
}

I only get 1 item from the data array : [1] instead of [1,2,3]

Use pencil and paper to work your way through that algorithm and you'll see that (a >= dump.length) ain't ever going to be true. — nnnnnn
– nnnnnn, Commented Nov 3, 2015 at 5:44
Answer is not the only key, but approach is important. So I suggest you to put console.log statement and just debug it because it looks like you are missing something (in terms of programming logic). — Gaurav Gupta
– Gaurav Gupta, Commented Nov 3, 2015 at 5:46

Anik Islam Abhi · Accepted Answer · 2015-11-03 05:48:18Z

1

That's becuase this line

if (a >= dump.length) {
    dump.push(data[i])
}

You pushed data when a is greater then or equal to dump.length

but in your loop

a < dump.length

It won't make it there

Try like this

for (var a = 0; a < dump.length; a++) {
    if (dump[a] == data[i]) { // when found break there
        break;
    }
}
if (a == dump.length) // if nothing found loop will be fully executed
    dump.push(data[i]);

JSFIDDLE

edited Nov 3, 2015 at 5:48

answered Nov 3, 2015 at 5:43

Anik Islam Abhi

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2 Comments

Ramesh Khadka Over a year ago

I wanted to push the data item into the dump array only when all the dump item is checked so a >= dump.length is used. I suppose a will be incremented by 1 greater than dump.length at the end of loop (a++)

Anik Islam Abhi Over a year ago

check my fiddle @RameshKhadka

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