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

• To: mathgroup at smc.vnet.net
• Subject: [mg6693] Re: Changing only Y's in a list of points: How?
• From: Yaroslaw Bazaliy <yar at leland.stanford.edu>
• Date: Fri, 11 Apr 1997 01:49:49 -0400 (EDT)
• Organization: Stanford University
• Sender: owner-wri-mathgroup at wolfram.com

```David S. Pieczkiewicz wrote:
>
>    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 would to it this way:

In[1]:=
l={{x1,y1},{x2,y2},{x3,y3},{x4,y4},{x5,y5}}
Out[1]=
{{x1,y1},{x2,y2},{x3,y3},{x4,y4},{x5,y5}}

In[2]:=
m=Transpose[l]
Out[2]=
{{x1,x2,x3,x4,x5},{y1,y2,y3,y4,y5}}

In[3]:=
n={m[[1]],m[[2]]+u}
Out[3]=
{{x1,x2,x3,x4,x5},{u+y1,u+y2,u+y3,u+y4,u+y5}}

In[4]:=
newl=Transpose[n]
Out[4]=
{{x1,u+y1},{x2,u+y2},{x3,u+y3},{x4,u+y4},{x5,u+y5}}

And then you can combine the four steps in one:
newl = Transpose[ {Transpose[l][[1]], Transpose[l][[2]] + u} ]

Yaroslaw.

```

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