[Maxima] flatten() extended functionality
ziga.lenarcic at gmail.com
Fri May 15 06:24:47 CDT 2009
I think this is a great idea (negative arguments - very neat).
Implementation is a bit more complex though than the usual case.
Adding a 'flatten_at' is not too hard probably. It can be a new
function or it can be the existing (I would prefer that) 'flatten'
with a new calling form:
flatten( mylist, ); to perform flattening only at level 2 or even
flatten( mylist, [2,4]); to flatten only levels 2 and 4.
I can be done (my lisp skill aren't exactly great though - the
resulting code would probably be too C-like).
I would like to see all these 'extensions' to flatten() in Maxima. If
noone is voulenteering for extending flatten in such ways, then maybe
I can try.
On 15. May, 2009, at 1:14 PM, reyssat wrote:
> It might be useful to flatten "inside first"
> aa:[[a,b], [[c]], d, [[h],[[d],s]]];
> flatten(aa,-3) --> [[a,b], [[c]], d, [[h],[d,s]]]
> flatten(aa,-2) --> [[a,b], [c], d, [h,d,s]]
> flatten(aa,-1) --> [a,b, c, d, h,d,s]
> In usual situations (homogenous levels), "map(flatten())" will do
> the job but maybe inefficiently.
> One can also imagine some mixed cases (flatten the "deep but not
> too deep" objects), but it is probably too rarely useful do spend
> too much work on this.
> Eric Reyssat
> Žiga Lenarčič a écrit :
>> I've sent this email to Starvos (since he is the copyright holder
>> of nset.lisp) a couple of days ago, but I haven't gotten any
>> response. Therefore I'm sending this on maxima mailing list.
>> I've modified $flatten in nset.lisp:
>> (defun flattenl-op (e op num)
>> (mapcan #'(lambda (e)
>> (cond ((or (= num 0) (mapatom e) (not (alike1 (mop e) op)))
>> (list e))
>> (t (flattenl-op (margs e) op (1- num)))))
>> (defun $flatten (e &optional (num nil))
>> (unless (and (not (null num)) (integerp num) (> num -1))
>> (merror "flatten: Second argument must be a non-negative
>> integer: ~M" num))
>> (when (null num) (setf num -1))
>> (cond ((or (= num 0) (specrepp e) (mapatom e)) e)
>> (t (mcons-op-args (mop e) (flattenl-op (margs e) (mop e)
>> It works as before for flatten(expr). For 'flatten(expr, num)'
>> the result is, that flatten 'flattens' 'num' times:
>> %i84: aa:[[a,b], [[c]], d, [[h],[[d],s]]];
>> %o84: [[a,b],[[c]],d,[[h],[[d],s]]]
>> %i134: flatten(aa,1);
>> %o134: [a,b,[c],d,[h],[[d],s]]
>> %i135: flatten(aa,2);
>> %o135: [a,b,c,d,h,[d],s]
>> %i136: flatten(aa,3);
>> %o136: [a,b,c,d,h,d,s]
>> My lisp sucks (feel free to rewrite), I know, but what do you
>> think about the functionality? This would breach the gap between
>> table and create_list output, as
>> flatten( table(i+j,[i,3],[j,3]) , 1) == create_list(i+j, i,1,3, j,
>> Also such flatten functionality can come in handy in many places
>> when working with lists of perhaps coordinates [x,y,z] and you
>> don't want to flatten out the whole list all together...
>> I can include this to CVS if I get developer access... Otherwise
>> it would be nice if someone did it instead of me.
>> Ziga Lenarcic
>> Maxima mailing list
>> Maxima at math.utexas.edu
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