[BASIC] List routine for eliminating values

[Moose]

Hello Does anyone know if there is a routine for eliminating identical values from a list:

Turning this:

{1,2,2,2,3,3,4,5,6

into {1,2,3,4,5,6

and this:

{1,2,3,4,5,6,2

into

{1,2,3,4,5,6

[King Harold]

I know a way, but it is rather inefficient
For each element, add it to a new list unless it is already in there (which can be checked with something like If not(max(LIST=newval) Then add End)
If your lists were strictly sorted it would be easier.. Sorting it first and using a better routine ("If not(last=new) Than add End") may be better, give it a try?

Of course someone else knows a good trick so I'd wait for them

ps: the code given is pseudo-basic and obviously you'll have to rename the variables: last could be L1(dim(L1)) for example

[Moose]

Thanks, I was temporarily obsessed with making the fastest polynomial solver I could imagine (no loops, just a crap load of list operations)

In he end I got the right answers (and then I got more of those right answers in the same list in a different order), but I didn't want to ruin it with a for( loop at the end

Basically when I typed in:

POLY
order=3

(clrhome)

a3^3+...+a0=0
a3=1
a2=0
a1=-7
a0=-6

and It gave me something like

{-3,-3,2,1,1,1}

BTW if you haven't noticed I'm a big fan of the ti 86

[King Harold]

I don't see a way around a loop here.. (unless you'd use recursion but that's a bit loopy - and that's not something you'd want to do in BASIC)
You could write an assembly program to do it for you, it will also loop but an assembly loop is much faster than a BASIC loop

[Moose]

I don't see a way around a loop here.. (unless you'd use recursion but that's a bit loopy - and that's not something you'd want to do in BASIC)
You could write an assembly program to do it for you, it will also loop but an assembly loop is much faster than a BASIC loop

Thats a good idea, I'll give it a try...

[kalan_vod]

Placing it in a loop would be a little slow, but math programs are easier in basic than asm..You just have to decide speed vs. size, if you want to have speed just make it all in asm

[Art_of_camelot]

hmm... you could check it at the time the variable is stored to the list, but it would still require a For loop to run through the list. This would work only if the elements of the list are stored one at a time.

[King Harold]

Checking whether a given element is in a list does not require a For loop
example:

Code: Select all

If max(L1=A)

(tested on my TI84 to be approx. 63 times as fast as a for loop over the same elements)

The problem is that when you have the entire list already, you'll have to do this for every element. Max has a loop inside it of course, but that's hopefully an assembly loop (I hope TI didn't decide to build some of their functions on top of other BASIC functions.. that would be terribly inefficient)

[driesguldolf]

I think it's hybrid... max() seriously degenerates if you have a bunch of elements (say, 200). In assembly this would still be lightning fast but for some idiot reason it isn't...

[King Harold]

I tested it on 999 elements..

[driesguldolf]

Nah, I was thinking of another function.
Btw, have you tested it with a list filled with zeros or random numbers?

[King Harold]

1 through 999
compared with 8

[driesguldolf]

Nevermind, I mistook it with the string functions.

[Art_of_camelot]

Checking whether a given element is in a list does not require a For loop

Ah, I wasn't familar with the "max" command. That's actually fairly useful, especially since it's faster.

[kalan_vod]

Might I suggest looking at this site, it has useful information for the beginner and advanced user.