Re: How to reverse sign on the y's in a list of (x, y)'s?

*To*: mathgroup at smc.vnet.net*Subject*: [mg61284] Re: How to reverse sign on the y's in a list of (x, y)'s?*From*: Bill Rowe <readnewsciv at earthlink.net>*Date*: Fri, 14 Oct 2005 05:55:16 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

On 10/13/05 at 1:39 AM, sherifffruitfly at gmail.com wrote: >Import from excel gives me a list of ordered pairs, and I want the >2nd element of each pair to be of opposite sign. Sticking the >negative sign in front of the entire Import statement reverses both >the 1st and the 2nd elements (duh). How do I get just the second >item to reverse sign? There are a variety of ways to do this. First, to generate some data In[1]:= data = Table[{Random[], Random[]}, {5}]; Using Map In[2]:= ({First[#1], -Last[#1]} & ) /@ data Out[2]= {{0.9429272001031446, -0.737894083389935}, {0.3224339596386182, -0.08532310093771701}, {0.25461414573678764 -0.24081290477367653}, {0.38201984290511914, -0.25350600514488736}, {0.7548652608303964, -0.6396949615917464}} Using matrix multiplication In[3]:= data . {{1, 0}, {0, -1}} or using Transpose In[4]:= {x, y} = Transpose[data]; Transpose[{x, -y}] and I am sure there are other ways I haven't thought of. -- To reply via email subtract one hundred and four