I want to slice elements of one array into a new left and right array. I am stuck on how to start this.
6 Answers
You'll want to start with the "slice" method. Note that it returns a NEW array without changing the old array, so you'll want to go back and mutate the old array as well.
For instance:
var a = [1,2,3,4,5],
b = a.slice(3);
a.length = 3;
// a is now [1,2,3]
// b is now [4,5]
4 Comments
jondavidjohn
you note that the original array won't change, but then in your example you show it changed???
Chris Nielsen
Yep. It's three lines, try it yourself. =)
Chris Nielsen
Line three (a.length = 3) changes the original array.
jondavidjohn
ahh, you're manually setting the length, missed that, thought you were saying that a.length was 3.
Given this array:
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
If you want to split the array so that the first 4 items go to the left array and the rest to the right array, then do this:
var leftArr = arr.slice(0, 4);
and
var rightArr = arr.slice(4);
You can make a function that returns those two arrays based on the split-position:
function splitArr(arr, i) {
return [ arr.slice(0, i), arr.slice(i) ];
}
Comments
umm..... have you looked at .slice() ?
new_array = your_array.slice( start_index , end_index );
This creates a completely new array, not a reference.
Comments
I'd use splice.
var a=[1,2,3,4,5,6];
var b=a.splice(3,a.length);
now a= [1,2,3]
and b=[4,5,6]
3 Comments
Šime Vidas
Just
var b = a.splice(3); is fine too. The second argument is not needed.
kennebec
@Šime Vidas- that's what I thought, until I tried it in IE. IE (before version 9) does nothing to the array and returns an empty array, without the second argument.
Šime Vidas
You're right. This is odd. Microsoft's own reference states that the second argument is optional. Btw, I also checked the old ECMAScript spec (ES3 from 1999.) - same thing. This feature is old, I have no idea why Microsoft didn't implement it until IE9.
From http://www.w3schools.com/jsref/jsref_slice_array.asp :
Syntax :
array.slice(start, end)
Example :
<script type="text/javascript">
var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.write(fruits.slice(0,1) + "<br />");
document.write(fruits.slice(1) + "<br />");
document.write(fruits.slice(-2) + "<br />");
document.write(fruits);
</script>
Output :
Banana
Orange,Apple,Mango
Apple,Mango
Banana,Orange,Apple,Mango
Comments
<html>
<body>
<script type="text/javascript">
var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.write(fruits.slice(0,1) + "<br />"); //Banana
document.write(fruits.slice(1) + "<br />"); //Orange,Apple,Mango
document.write(fruits.slice(-2) + "<br />"); //Apple,Mango
document.write(fruits); //Banana,Orange,Apple,Mango
</script>
</body>
</html>
(Reference from w3schools): http://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_slice_array
:)