Re: list manipulation

*To*: mathgroup at smc.vnet.net*Subject*: [mg100132] Re: [mg100122] list manipulation*From*: "David Park" <djmpark at comcast.net>*Date*: Tue, 26 May 2009 05:07:36 -0400 (EDT)*References*: <200905191101.HAA07313@smc.vnet.net> <gv0gn0$a19$1@smc.vnet.net> <20101854.1243249205388.JavaMail.root@n11>

The Presentations package from my web site ($50) has a command in the Manipulations section named MapLevelParts that does what you want. MapLevelParts[function, {topposition, levelpositions}][expr] will map the function onto the selected level positions in an expression. Levelpositions is a list of the selected parts. The function is applied to them as a group and they are replaced with a single new expression. Other parts not specified in levelpositions are left unchanged. Example: a + b + c + d + e // MapLevelParts[f, {{2,4,5}}] -> a + c + f[b + d + e] For your case we could do it as follows: testlist = RandomInteger[{-10, 10}, {5, 5}] {{6, 4, 5, -5, -2}, {-3, -5, -8, 9, -3}, {6, -2, -3, 8, -4}, {4, 10, 2, -6, 9}, {-2, -7, 4, 4, -7}} MapLevelParts[f @@ # &, {{3, 4}}] /@ testlist {{6, 4, f[5, -5], -2}, {-3, -5, f[-8, 9], -3}, {6, -2, f[-3, 8], -4}, {4, 10, f[2, -6], 9}, {-2, -7, f[4, 4], -7}} David Park djmpark at comcast.net http://home.comcast.net/~djmpark/ From: Scot T. Martin [mailto:smartin at seas.harvard.edu] 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>