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MathGroup Archive 2007

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Re: How to subtract two sets of data for a ListPlot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg76749] Re: How to subtract two sets of data for a ListPlot
  • From: Bill Rowe <readnewsciv at sbcglobal.net>
  • Date: Sat, 26 May 2007 04:51:30 -0400 (EDT)

On 5/25/07 at 6:45 AM, dmilioto at comcast.com (chuck009) wrote:

>Hi all.  Suppose I've calculated two sets of lists of the form for
>example:

>list1={{1,1},{2,2},{3,3}};

>list2={{1,1},{2,4},{3,9}};

>What's an efficient way to create a third list with the same
>x-values but with the y-values subtracted

>newlist={{1,0},{2,-2},{3,-6}};

>I realize I can manually subtract them in a For-loop, but I'm sure a
>one-line command using Map or some other construct can be used as
>well but can't figure it out.

Yes, you definitely want to avoid For loops. Here are two ways.
=46irst using pattern matching

In[3]:= Transpose[{list1, list2}] /. {{a_, b_}, {_, c_}} -> {a,
    b - c}

Out[3]= {{1, 0}, {2, -2}, {3, -6}}

second using functional programming

In[4]:= MapThread[{First[#1], Last[#1 - #2]} & , {list1, list2}]

Out[4]= {{1, 0}, {2, -2}, {3, -6}}

And I am sure others will show you still more ways to do the
same thing
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