Re: Replacing Numbers in a List
- To: mathgroup at smc.vnet.net
- Subject: [mg68259] Re: [mg68230] Replacing Numbers in a List
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Mon, 31 Jul 2006 03:45:12 -0400 (EDT)
- Reply-to: hanlonr at cox.net
- Sender: owner-wri-mathgroup at wolfram.com
y={122,211,212,221,223,232,322};
x=Table[Random[Integer,{100,325}],{10^5}];
Count[x,222]
452
x1=x;Timing[Do[x1=ReplacePart[x1,222,Position[x1,y[[i]]]],{i,Length@y}];]
{0.450666 Second,Null}
Timing[x2=x/.x_?(MemberQ[y,#]&):>222;]
{1.62676 Second,Null}
Timing[x3=ReplacePart[x,222,Position[x,_?(MemberQ[y,#]&)]];]
{1.55927 Second,Null}
Timing[x4=If[MemberQ[y,#],222,#]&/@x;]
{0.154602 Second,Null}
Count[x1,222]==Count[x2,222]==Count[x3,222]==Count[x4,222]
True
Of these, mapping the If statement is best.
Bob Hanlon
---- Gregory Lypny <gregory.lypny at videotron.ca> wrote:
> Hello everyone,
>
> 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?
>
> Regards,
>
> Gregory
>