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Order of first number

OpenMusic
#1

Hello, OMians!

I wonder whether there is a simple and efficient way to perform the following test: in a list of lists of numbers, in each list I would like to test that a larger number does not appear before a lower one (the first time only). For example: (1 2 3 2 1) is ok, but (1 3 2 1 2) not, because 3 appears before 2 appears the first time. Other examples of not good lists are: (2 1 3 1 2 3 2), first 2 before 1, (1 2 4 3 2 5 1), 4 before 3, (1 2 1 1 3 1 5 1 1 4 2), 5 before 4.
What I managed to write looks terribly complicated to me, but, perhaps, there is no easy solution to this.
Thank you very much in advance.

Marco

#2

Hi Marco!

Not sure what you consider sequence manipulations as efficient, but if you #'remove-duplicates on your list, you can check whether the result is ordered. Perhaps something like this:

(let ((seq (remove-duplicates '(1 2 1 1 3 1 5 1 1 4 2) :from-end t)))  
    (every #'< seq (cdr seq)))
#3

Hi Marco!

Not sure whether you consider sequence manipulations as efficient, but if you #'remove-duplicates on your list, you can check whether the result is ordered. Perhaps something like this:

(let ((seq (remove-duplicates '(1 2 1 1 3 1 5 1 1 4 2) :from-end t)))  
    (every #'< seq (cdr seq)))
#4

Thank you very much for your proposal. Actually, it’s great!! I was doing loops of loops, really not efficient at all. I will try it immediately.

Marco