Re: Replacing Numbers in a List
- To: mathgroup at smc.vnet.net
- Subject: [mg68269] Re: Replacing Numbers in a List
- From: "Ray Koopman" <koopman at sfu.ca>
- Date: Mon, 31 Jul 2006 03:45:36 -0400 (EDT)
- References: <eahsgh$op1$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Gregory Lypny wrote:
> I have a long list of integers called x, and I want to replace those
> that are members of list y with the number 222.
>
> I did it this way with a Do loop.
>
> y = {122, 211, 212, 221, 223, 232, 322};
> Do[x = ReplacePart[x,222, Position[x, y[[i]]]],{i, Length@y} ]
>
> Is this OK, or is there a more direct way?
Map[If[MemberQ[y,#],222,#]&,x] gives the modified list directly.
But note that it doesn't automatically overwrite the old list.
You must do that explicitly: x = Map[...].