Randomize playlist

Archived
1

Hi guys
I am trying to randomize the entries in a photo playlist array. It seems to work fine except for some reason the last 3-4 entries do not randomize to the new array - they’re chopped off.
I am looping through the playlist array, and after I randomly find and copy an entry to a new array, I delete the array entry so it won’t be used again.

According to the documentation, the RND function should randomize between 0 and 1. So if I perform RND(1), shouldn’t the result be 0 or 1? Or, RND(3) result be 0,1,2, or 3?

Here is a sample of my print output:

ext1:/Photos/1.jpg
ext1:/Photos/2.jpg
ext1:/Photos/3.jpg
ext1:/Photos/4.jpg
ext1:/Photos/5.jpg
ext1:/Photos/6.jpg
ext1:/Photos/7.jpg
ext1:/Photos/8.jpg
ext1:/Photos/9.jpg
ext1:/Photos/10.jpg

Length of playlist = 10

(Length of playlist : random array position > new array position)
10 : 7 > 0
9 : 2 > 1
8 : 6 > 2
7 : 1 > 3
6 : 5 > 4
5 : 2 > 5

Sample code:

index = 0
for each item in playlist_master
’ Calculate the new length of the master playlist
playlist_master_count = playlist_master.count()
if playlist_master_count > 0
’ Get a random index value
random_index = RND(playlist_master_count)
’ Get playlist item from master playlist based on random index value
playlist_item = playlist_master[random_index]
’ Copy the playlist item to the new randomized playlist
playlist_random.Push(playlist_item)
’ Remove the copied playlist item from master so it isn’t copied again
playlist_master.Delete(random_index)
else
‘Just copy last entry’
playlist_item = playlist_master[playlist_master_count]
playlist_random.Push(playlist_item)
playlist_master.Delete(playlist_master_count)
end if
’ Log playlist processing
print playlist_master_count;" :“;random_index;” >";index
index = index + 1
end for

Thanks for any suggestions
AC

2

Rnd(3) will produce values of 1, 2, or 3. Never 0, so you should pull your random index with:

random_index = RND(playlist_master_count) - 1
3

“TheEndless” wrote:
Rnd(3) will produce values of 1, 2, or 3. Never 0, so you should pull your random index with:

random_index = RND(playlist_master_count) - 1

Thanks for the -1 tip, which makes total sense in order to reach the array at index [0].

My loop still exits with 3 or 4 items remaining if I use a random index. If I delete items at index [0] on each loop instead, all the items in the array are transferred to the new array.

I created a separate array with static items just to test this. I get the same strange result where the loop does not finish.

Losing my mind.

4

Found the answer.

This loop will work:
for i=1 to playlist.count() step 1

This loop will not, it will cut itself short for some unknown reason: (to waste my time)
for each item in playlist.count()

5

foreach won’t work correctly if you delete entries in the array while traversing it. You may want to look at the Fisher-Yates shuffling algorithm, which is a simple way to shuffle an array in-place.


function Shuffle(array as Object) as Void
    for i% = array.count()-1 to 1 step -1
        j% = Rnd(i% + 1) - 1
        t = array[i%] : array[i%] = array[j%] : array[j%] = t
    end for
end function

–Mark

6

“RokuMarkn” wrote:
foreach won’t work correctly if you delete entries in the array while traversing it. You may want to look at the Fisher-Yates shuffling algorithm, which is a simple way to shuffle an array in-place.


function Shuffle(array as Object) as Void
    for i% = array.count()-1 to 1 step -1
        j% = Rnd(i% + 1) - 1
        t = array[i%] : array[i%] = array[j%] : array[j%] = t
    end for
end function

–Mark

Thanks a lot for this idea! From 14 to 4 lines of code, nice!

AC