Tell me more ×
Stack Overflow is a question and answer site for professional and enthusiast programmers. It's 100% free, no registration required.
up vote 0 down vote favorite

I am attempting to populate array:

var array2 = ["a", "b", "c"];

With some random number/value, so that the value separates each original value. However, using a for loop like this:

for (var am = 1; am < array2.length; am+2) {
   array2.splice(am, 0, undefined);
}

Causes my browser to freeze, since on each splice the array2's length mutates and causes an infinite loop so I attempted this method:

var l = array2.length;

for(var i = 1; i < l; i+2) {
   array2.splice(i, 0, undefined);
}

Now I don't know what's going on. I assume l is mutating again.

I have to advance i for two because array2 after the first splice becomes:

["a", undefined, "b", "c"];

However, since i = 3 and I've set the expression i < l, the only explanation is that l is changing again.

Any explanation would be welcome. The end result of how I want the code to proceed is:

array2 = ["a", undefined, "b", undefined, "c"];
share|improve this question

3 Answers

up vote 3 down vote accepted 
for (var am = 1; am < array2.length; am+2) {

You're not actually incrementing am in that line. Change it to:

for (var am = 1; am < array2.length; am+=2) {

Using += means am = am + 2

share|improve this answer
Oops, I probably never used anything else than am++ so I forgot about that one. – User2121315 Jan 11 at 11:13
Aye, now my first attempt works perfectly, thank you! – User2121315 Jan 11 at 11:15
up vote 1 down vote

You could try this:

var array2 = ["a", "b", "c"];

var l = array2.length;

// Stop 1 item before the end and set steps of 1 item
for(var i = 0; i < (l - 1); ++i) {
   // You inserting starting from index 1 and move 2 items ahead for each element
   array2.splice(1 + (i * 2), 0, undefined);
}
share|improve this answer
1  
Or just while(--l>0){array2.splice(l,0,undefined);} – David Jan 11 at 11:19
Haha, "almost". – User2121315 Jan 11 at 11:22
yea, that's actually a much nicer notation :) – user1 Jan 11 at 11:23
up vote 0 down vote

You can do it with:

var array2 = ["a", "b", "c"],
    length = array2.length,
    output = [];

for ( var i = 0; i < length; i++ ) {
  output.push(array2[i]);
  if ( i < length - 1 ) {
    output.push(undefined);
  }
}

// output:
// ["a", undefined, "b", undefined, "c"]
share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.