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I want to delete every second and third element from an array in Javascript.

My array looks like this:

var fruits = ["Banana", "yellow", "23", "Orange", "orange", "12", "Apple", "green", "10"];

Now I want to delete every second and third element. The result would look like this:

["Banana", "Orange", "Apple"]

I tried to use a for-loop and splice:

for (var i = 0; fruits.length; i = i+3) {
    fruits.splice(i+1,0);
    fruits.splice(i+2,0);
};

Of course this returns an empty array because the elements are removed while the loop is still executed. How can I do this correctly?

Thank you.

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There's a couple of things wrong, particularly that this is the equivalent of running while(fruits), which will run for as long as fruits evaluates to true, instead of just going through the array once. – yahelc Nov 29 '10 at 21:34

5 Answers

up vote 6 down vote accepted

You could approach this from a different angle and push() the value you don't want deleted into another Array:

var firstFruits = []

for (var i = 0; i < fruits.length; i = i+3) {
    firstFruits.push(fruits[i]);
};

This approach may not be as terse as using splice(), but I think you see gain in terms of readability.

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I'd prefer the first over the second, as the second will produce an array like ["Banana","","","Orange","","","Apple"] – Robert Nov 29 '10 at 21:50
@Robert, you're absolutely right. I'm sure that's not functionality the OP desires. Thanks, I'll update my response to just include the first one. – McStretch Nov 29 '10 at 21:54
Wow, that's easy. Thank you very much. :-) – Bob Nov 29 '10 at 21:58
up vote 7 down vote

This works for me.

var fruits = ["Banana", "yellow", "23", "Orange", "orange", "12", "Apple", "green", "10","Pear","something","else"];

for(var i = 0; i < fruits.length; i++) {
    fruits.splice(i+1,2);
}

//fruits = Banana,Orange,Apple,Pear

Here's a demo that illustrates it a little better: http://jsfiddle.net/RaRR7/

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That's also a really good idea, thank you. – Bob Nov 29 '10 at 22:08
up vote 1 down vote

Try looping through the array in reverse order

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up vote 0 down vote

Have you considered just copying the first, fourth, and seventh elements to a new array? It isn't very memory efficient but it'll still work fine.

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up vote 0 down vote

You'll want to move through the array backwards, then if i % 2 == 0 || i%3 == 0 then splice the element from the array

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