Re: how to sum lists of unequal length?
- To: mathgroup at smc.vnet.net
- Subject: [mg70421] Re: how to sum lists of unequal length?
- From: Peter Pein <petsie at dordos.net>
- Date: Mon, 16 Oct 2006 02:34:15 -0400 (EDT)
- References: <egq2th$84h$1@smc.vnet.net>
Arkadiusz.Majka at gmail.com schrieb:
> Hi all,
>
> I have lists of unknown and unequal lengths. I want to sum them, e.g
>
> {a1,a2,a3}+{b1,b2,b3,b4,b5} and obtain result
> {a1+b1,a2+b2,a3+b3,b4,b5}. Simply filling by zeros of the shorter list
> is impossible because I have no idea how many zeros I have to pad.
>
> Please, help
>
> Arek
>
Hi Arek,
you don't need to have an idea, because Mathematica can easily estimate the
maximal length of the lists to sum:
In[1]:= (* generate 3 Lists of length 3, 7 and 5 resp. *)
myLists=Inner[Map[#1,Range[#2]]&,{a,b,c},{3,7,5},List]
Out[1]=
{{a[1],a[2],a[3]},
{b[1],b[2],b[3],b[4],b[5],b[6],b[7]},
{c[1],c[2],c[3],c[4],c[5]}}
and this determines the maximal length, pads an appropriate number of zeros to
the shorter lists and adds them:
In[2]:=
Total[PadRight[#,Max[Length/@myLists]]&/@myLists]
Out[2]=
{a[1]+b[1]+c[1],a[2]+b[2]+c[2],a[3]+b[3]+c[3],b[4]+c[4],b[5]+c[5],b[6],b[7]}
Easy, isn't it? :-)
Greetings,
Peter