Re: list manipulation

*To*: mathgroup at smc.vnet.net*Subject*: [mg100199] Re: list manipulation*From*: Ray Koopman <koopman at sfu.ca>*Date*: Thu, 28 May 2009 04:26:38 -0400 (EDT)*References*: <200905191101.HAA07313@smc.vnet.net> <gv0gn0$a19$1@smc.vnet.net>

Join[ Take[#,n], {f[#[[n+1]],#[[n+2]]]}, Drop[#,n+2] ]& /@ data If f can operate on lists then Transpose@Join[ Take[#,n], {f[#[[n+1]],#[[n+2]]]}, Drop[#,n+2] ]& @ Transpose@data should be faster. On May 25, 3:17 am, "Scot T. Martin" <smar... at seas.harvard.edu> wrote: > I'm wondering if anyone has bright ideas on the puzzle below. I'm trying > to take a very large list of the following form: > > {{.., .., a, b, ..},{.., .., c, d, ..},..} > > into the form > > {{.., .., f[a, b], ..},{.., .., f[c, d], ..},..} > > It seems to me that there must be some clever and beautiful way to do this > that I haven't thought of. My code is below with two clumsy solutions. > > Suggestions on how to do better? > > My code: > > In[1]:= (*shown here as minimal to define problem but actual list has \ > large N and many entries*) > > data = {{element11, element12, element1N, target11, target12, > element1N3, element1N4}, {element21, element22, element2N, > target21, target22, element2N3, element2N4}}; > > In[2]:= (* first clumsy approach *) > > Replace[data, list : _List :> {Sequence @@ list[[1 ;; 3]], > Sequence[f[list[[4 ;; 5]]]], Sequence @@ list[[6 ;;]]}, {1}] > > Out[2]= {{element11, element12, element1N, f[{target11, target12}], > element1N3, element1N4}, {element21, element22, element2N, > f[{target21, target22}], element2N3, element2N4}} > > In[3]:= (* second clumsy approach *) > > data /. {a : Repeated[_, {3}], b : Repeated[_, {2}], > c : __} -> {a, f[b], c} > > Out[3]= {{element11, element12, element1N, f[target11, target12], > element1N3, element1N4}, {element21, element22, element2N, > f[target21, target22], element2N3, element2N4}}

**References**:**Are you wolfing tonight?***From:*magma <maderri2@gmail.com>