Use automator to select every 3rd file to move to new folder?

Question

I have an interesting 'problem' I think.
As a result of a time-lapse experminent, I have a folder which holds several thousands of pictures from a fixed point, made over several days & nights.
But there is one issue: the camera made 3 different exposures every 5 seconds.
This resulted in every 3rd picture 'belonging' to each other. So these have to be selected for going in a seperate folder. Menaing: pictures 1 and 4 and 7 and 10 .... they must go in one folder. 2 and 4 and 8 and 11.. in the second folder. Finally 3 and 5 and 9 and 12 in a third folder.
How to do this with software (to avoid injury) because of the thousands of pics.
Is this do-able with automator? How?
Tnx

Answer 1

This has come up a few times, so I tweaked one of my Automator actions a while back to do this. I thought I had uploaded it before, but the latest version of my *Trim Input Items* action is available on my iDisk here. It keeps or trims the input list to the selected number of items from the beginning, end, interval, or random locations. You may need to sort the input file list to get them into the desired order, since the action just works with the items in the list, and doesn't care what they are.
I haven't tested it with large file lists, but an example workflow using my action would be:
1) *Get Specified Finder Items* (or however you want to get the file items)
2) *Set Value of Variable* { Variable: _File List_ }
3) *Trim Input Items* { Keep Interval 3 items, starting from item 1 }
4) *Move Finder Items* { To: _First Location_ } -- move first batch
5) *Get Value of Variable* { Variable: _File List_ } (Ignore Input)
6) *Trim Input Items* { Keep Interval 3 items, starting from item 2 }
7) *Move Finder Items* { To: _Second Location_ } -- move second batch
8) *Get Value of Variable* { Variable: _File List_ } (Ignore Input)
9) *Trim Input Items* { Keep Interval 3 items, starting from item 3 }
10) *Move Finder Items* { To: _Third Location_ } -- move third batch