Re: matrix problem
- To: mathgroup at smc.vnet.net
- Subject: [mg107114] Re: matrix problem
- From: Peter Pein <petsie at dordos.net>
- Date: Wed, 3 Feb 2010 06:09:38 -0500 (EST)
- References: <hk93ca$f68$1@smc.vnet.net>
Am 02.02.2010 12:47, schrieb Piotr Munik: > Dear Math Group, > > I have matrix M and matrix N > for example > M={{1,2},{3,4},{5,6},{7,8}} > N={{1,8},{5,0},{9,7}} > (dimension is diffrent) > I need to make new matrixes which include only this rows from matrix M and > matrix N for which firsts elements are the same in both matrix (M and N). > so I need > M1={{1,2},{5,6}} > N1={{1,8},{5,0}} > Elements of matrix are real (not always integer) > Please for help > Peter > > Hi Peter, 1.) do not use reserved function names ("N" in this case) as variables; this might lead to "surprises". 2.) In[1]:= mM={{1,2},{3,4},{5,6},{7,8}}; mN={{1,8},{5,0},{9,7}}; The following call to Pick[] works on both matrices at once: In[3]:= {mM1,mN1}= Pick[#,Map[First,#,{2}], Alternatives@@Intersection@@([[All,All,1]])]&[{mM,mN}] Out[3]= {{{1,2},{5,6}},{{1,8},{5,0}}} Greetings, Peter