# [Maxima] select all x in L

Wolfgang Lindner LindnerW at t-online.de
Thu May 24 06:48:00 CDT 2007

```Dear Mario, Stavros, Daniel and Richard,

Indeed, the extended clever use of sublist or arryinfo was surprising for me. Once seen
it's clear.

Thanks for kindly coaching me.
HTH Wolfgang

"Richard Fateman" <fateman at cs.berkeley.edu> schrieb:
> I don't know what the elements of the list V_ look like.  If they are all
> symbols, like x y z then
> you could try
> ans:0\$
> for i in V do ans:ans+i\$
>
> Then the list looks like 3*z+4*y+x    etc.  And you can make it into a list
> [3*z,4*y,x]
> By using substpart(ans,0,"["). Or you can pick out the coefficients by using
> coeff.
>
>
> Or if the elements are numbers, try
> For i in V do ans:ans+histogram[i].
>
> The algorithm you propose is quite inefficient, but maybe that doesn't
> matter to you.
>
> You could also sort the list, and then count the runs.
>
> Or you could do    for i in V do histogram[i]:histogram[i]+1,   and then
> look at arrayinfo(histogram).
>
>
>
> RJF
>
>
> > -----Original Message-----
> > From: maxima-bounces at math.utexas.edu
> > [mailto:maxima-bounces at math.utexas.edu] On Behalf Of Wolfgang Lindner
> > Sent: Wednesday, May 23, 2007 2:32 PM
> > To: maxima-help
> > Cc: Sebastian Scigala
> > Subject: [Maxima] select all x in L
> >
> > dear group,
> >
> > currently we (me and my students) are studying a book on
> > elementary probability theory
> > (with use CAS DERIVE as assistent) and are porting some of
> > the code to (wx)Maxima 5.12.
> > Some of the basic concepts we will define ab ovo, before we
> > will switch to Mario
> > Riotorto's massive application package 'descriptive.mac' in
> > order to draw histograms etc.
> >
> > One early problem is to define the 'frequency of a in list v_'.
> > The Derive code is:
> >                      H(a, v_) := DIM(SELECT(x = a, x, v_))
> >
> > I defined the helper function
> > (%i1)  select(a,L) := block([LL:[]], for x in L do if x=a
> > then LL:cons(x,LL),LL)\$
> > (%i2)  select(2,[3,2,4,2]);
> > (%i3)  H(a,L):= length(select(a,L));
> > (%i4)  H(2,[3,2,4,2,5]);
> > (%o4)  2
> > which seems ok.
> >
> > Q1: is there a predefined function 'select' (with another
> > name?) in Maxima
> >     I have overlooked?
> > Q2: I would like to have a 'more functional and general'
> > version of select.
> >     Does a member of the Maxima community has some hints?
> >
> > --
> > HTH  Wolfgang
> >
> >
> > _______________________________________________
> > Maxima mailing list
> > Maxima at math.utexas.edu
> > http://www.math.utexas.edu/mailman/listinfo/maxima
```