Re: Apply a function to parts of a list

*To*: mathgroup at smc.vnet.net*Subject*: [mg110331] Re: Apply a function to parts of a list*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Sun, 13 Jun 2010 04:12:46 -0400 (EDT)

data = Thread[Array[#, 3] & /@ {x, y}] {{x[1], y[1]}, {x[2], y[2]}, {x[3], y[3]}} data /. {a_, b_} -> {a, b/2} {{x[1], y[1]/2}, {x[2], y[2]/2}, {x[3], y[3]/2}} {1, 1/2} # & /@ data {{x[1], y[1]/2}, {x[2], y[2]/2}, {x[3], y[3]/2}} {#[[1]], #[[2]]/2} & /@ data {{x[1], y[1]/2}, {x[2], y[2]/2}, {x[3], y[3]/2}} Bob Hanlon ---- Rui <rui.rojo at gmail.com> wrote: ============= I have always done very ugly code when trying to do something seemingly simple and basic such as applying a function to subparts of a list. Simple example, I want to divide by 2 all the second elements of a list {{a, 5}, {b, 6}, ...} --> {{a, 5/2}, ...} My ideas: Transpose -> MapAt/Map -> Transpose Build the sublist with Part and then rebuild it Use Map and a function like #[[All, 2]] and then rebuild it. I don't like any solution. I wanted to know if there's anything simple that I'm overseing Thanks guys