Re: Dot or Inner ... but not quite

*To*: mathgroup at smc.vnet.net*Subject*: [mg79644] Re: Dot or Inner ... but not quite*From*: mcmcclure at unca.edu*Date*: Wed, 1 Aug 2007 04:55:56 -0400 (EDT)*References*: <f8n2rc$lp9$1@smc.vnet.net>

On Jul 31, 6:27 am, "Diamond, Mark" <d... at dot.dot> wrote: > I have two equi-length lists, the first of number, the second of > (equi-length) lists of numbers , such as > l1={1,4,3}; > l2={{1,7},{1,9},{5,2}}; > I want to produce 1*{1,7}+4*{1,9}+3*{5,2} There are a number of ways to approach this and your technique looks fine to me. Inner doesn't work directly because it delves deeply into nested structures as you can see by executing something like: Inner[f, {{{a}, {c}}}, {{d, e}}, List] You can prevent this by changing the head at the appropriate level; you can always switch it back, if necessary. In your problem, you could use: l1 = {1, 4, 3}; l2 = {{1, 7}, {1, 9}, {5, 2}}; Inner[Times, l1, h /@ l2, List] /. h[x_] -> x You could also use Thread: Times@@@Thread[f[l1, l2]] If you are doing this for extremely long lists, timing tests indicate that the Thread technique is the fastest. Mark