Re: Apply a function to parts of a list
- To: mathgroup at smc.vnet.net
- Subject: [mg110318] Re: Apply a function to parts of a list
- From: Albert Retey <awnl at gmx-topmail.de>
- Date: Sun, 13 Jun 2010 04:10:24 -0400 (EDT)
- References: <huvk7i$rtn$1@smc.vnet.net>
Am 12.06.2010 11:32, schrieb Rui:
> 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
Here are two that I often use:
list = {{a, 5}, {b, 6}, {c, 7}};
Replace[list, {x_, y_} :> {x, y/2}, {1}]
{#1, #2/2} & @@@ list
where @@@ is a shortcat for Apply at level 1, see the documentation for
details...
hth,
albert