0

So it could just be I'm crazy tired but I can't seem to figure this out.

I've been picking up javascript which I'm finding horrible coming from actionscript 3 where everything was typed. I had a function that referenced two array variables directly, I later needed to use it again for a different data set so I've altered it to take parameters and now it's breaking.

I have one array full of elements, the 2nd is empty. When I call the function, a random element is removed from the first array and pushed into the 2nd array, that element is also returned by the function. If the 1st array is empty I have concat the 2nd array to fill it back up. The goal was to randomly iterate through the elements and not have the selected elements show up again until I had finished a full cycle.

Prior to concat I was using slice(which should work just as well?), the problem I believe is that I know have a parameter that is redefined when I do 'array = array2.slice()', concat doesn't seem to work around that. I don't know if returning the single sliced element from the first array is bad if I'm expecting a string, I think slice is returning an array with the single element, easy fix there though by adding [0] to the return statement.

Heres the code:

//Gets a random element from array, that element is moved from the 'src' array to the 'bin' array,
//this allows random selection without choosing the same element until all of 'src' array elements have been picked
function getRandomElement(array_src,array_bin){
    //Randomly selects a tweet from the que, then stores it in another array so each tweet shows once before recycling
    if(array_src.length==0 && array_bin.length>0) {array_src.concat(array_bin);} //Recycles array elements when the src array is empty
    var randomElement = array_src.splice(Math.floor(Math.random()*array_src.length),1); //Grab a random array element
    array_bin.push(randomElement);//array elements stored here to be recycled

    return randomElement;
}

I think I could maybe use an object with two properties pointing to the arrays and pass those in, though it'd be nicer if there is a better way. I could also use push on array_src looping through the array_bin to work around that issue if there isn't any other way.

I wouldn't say this is a duplicate Felix. The answer you provided is pretty much the same, but the question itself is phrased differently, I wasn't aware of the term mutate, finding the question/answer wouldn't be easy, none of the suggested links SO provided were relevant. Worth keeping up for making the answer more discoverable to those unaware of the mutate term.

Improve this question
3
  • Your update explains exactly why this question SHOULD be marked as a duplicate. For people that aren't aware of the terminology. This is a book keeping measure and not meant as a slight against you. Commented Aug 21, 2014 at 17:18
  • That's ok, I'm not very familiar with what the marked as duplicate meant, was thinking at the time I was asked to justify keeping the duplicate up otherwise it'd be deleted. I think I misunderstood that :) My point was to keep the question available so those who don't know the term mutate would come across this and learn. Commented Aug 22, 2014 at 12:33
  • No problem. Questions only get deleted if there are very poor quality (this isn't). Commented Aug 22, 2014 at 16:49

1 Answer 1

Reset to default
1

I have a hard time understanding the problem, but I think you are wondering why array_src.concat(array_bin) doesn't seem to do anything?

That's because .concat returns a new array. If you want to mutate the existing array_src array, you can use .push:

array_src.push.apply(array_src, array_bin);

FWIW, this has nothing to do with strong typing. JavaScript (and I guess ActionScript as well), is pass-by-value. That implies that assigning a new value to array_src doesn't change the value of the variable that was passed to getRandomElement.

But since arrays are mutable in JavaScript (and ActionScript I assume), you can mutate the array itself.

Improve this answer
Sign up to request clarification or add additional context in comments.

8 Comments

so concat would be similar to how I was handling it with slice? Since I'm not using the actual variable for the array but a paramter referencing it, array=array.concat(array2) would not update my actual array outside of the function. That's my problem.
a.concat(b) simply creates a new array containing all elements of a and b. It doesn't change a or b in any way. a.slice(i) also doesn't change a, it just returns a new array containing all elements of a starting at index i. I tried to explain why assigning a new value to array_src doesn't work (JavaScript is pass-by-value).
Apologies about the comment on strong typing, it's not relevant to the issue, but I do miss the benefits I had from having such. I tried your push.apply, it doesn't appear to be working. I'm seeing a single value within an array be stored. So [[value]] instead of [value, value, value, etc]
Oh, you also have to do array_bin.push(randomElement[0]); since .splice always returns an array.
I get why it doesn't work when I previously assigned it to array_src with the returned sliced array(I wasn't familiar with concat). Is there a proper way around this or do I need to store my arrays in an obj?
|

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.