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Re: Changing only Y's in a list of points: How?

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  • Subject: [mg6730] Re: [mg6665] Changing only Y's in a list of points: How?
  • From: Kristina Pawlikowski <pawlikk at>
  • Date: Sat, 12 Apr 1997 02:16:25 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

Clumsy, but I think that this works:


pointlist =

==>  {{x1,0.3+y1},{x2,0.3+y2}}

>   Hopefully, the subject line says it all. If not, here's what I'm trying
>to do. Suppose I have a list of points:
>   pointlist = { {x1,y1}, {x2,y2}, {x3,y3}, ..., {xn,yn} };
>   Of course, there are numbers instead of the above symbols, but you get
>the picture. Now, suppose I'd like to "raise" or "lower" this list, in
>effect, changing all the y's by a constant, but leaving the x's alone.
>   I know this can be done easily using a procedural construct, but I'm
>wondering if there's a functional equivalent, which is hopefully more
>elegant, faster, etc.
>   At first - and here, I wasn't thinking, and am almost embarassed to
>write this - I naively tried the following:
>   pointlist += 0.3;
>   Of course, 0.3 (which could be anything, really) ends up getting added
>to *all* members of all the sublists, which is not what I wanted. I've
>spent some time looking through the Mathematica (Phone)Book, as well as a
>few other sources, but I couldn't find an obvious way of solving the
>problem using Map[], Apply[], etc., to do the trick. It's probably trivial,
>but not being raised on Lisp, functional programming is still pretty new
>for me. Any suggestions?
>Thanks for your time,
>David S. Pieczkiewicz, B. A.                    david at
>Health Informatics Program                      dsp3 at
>Division of Health Computer Sciences            dsp3 at
>University of Minnesota, Twin Cities Campus     (612) 625-8440

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