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Topic: altering each member of a list that matches a certain pattern
Replies: 9   Last Post: Jun 22, 2012 3:03 AM

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 Vince Virgilio Posts: 135 Registered: 4/30/05
Re: altering each member of a list that matches a certain pattern
Posted: Jun 22, 2012 3:00 AM

On Wednesday, June 20, 2012 3:54:33 AM UTC-4, Jason Ebaugh wrote:
> Good people,
>
>
> I need to alter each member of a list that matches a certain pattern.
> However, I need the whole list back, in its original order.
> So Cases[] on its own doesn't do the trick.
>
> Here is a toy example that is analogous to my real problem:
> Put an asterisk on each value that is 10 or greater in the following list.
>
> list = RandomSample[Range[20], 20]
>
> Out[1]= {19, 16, 5, 13, 10, 20, 1, 3, 18, 8, 9, 6, 12, 7, 4, 15, 11, 14, 2, 17}
>
> I came up with two ways to do this.
> However, I feel like I may be missing a simpler, single function way to do this.
>
> Method 1:
> If[# > 9, SuperStar[#], #] & /@ list
>
> Out[2]= {SuperStar[19], SuperStar[16], 5, SuperStar[13], SuperStar[10],
> SuperStar[20], 1, 3, SuperStar[18], 8, 9, 6, SuperStar[12], 7, 4,
> SuperStar[15], SuperStar[11], SuperStar[14], 2, SuperStar[17]}
>
>
> Method 2:
> ReplacePart[list,
> Table[{Position[list, x_ /; x > 9][[i, 1]] ->
> Map[SuperStar, Cases[list, x_ /; x > 9]][[i]]}, {i,
> Length[Cases[list, x_ /; x > 9]]}] // Flatten]
>
> Out[3]= {SuperStar[19], SuperStar[16], 5, SuperStar[13], SuperStar[10],
> SuperStar[20], 1, 3, SuperStar[18], 8, 9, 6, SuperStar[12], 7, 4,
> SuperStar[15], SuperStar[11], SuperStar[14], 2, SuperStar[17]}
>
>
> Am I missing a more straightforward way to do this?
>
>
>
> Thanks,
> Jason
>
>
> Jason Ebaugh

There is also MapAt:

rs = RandomSample[Range[20], 20];
pos = Position[rs, _?(# > 9&)];
MapAt[SuperStar, rs, pos]

Date Subject Author
6/20/12 Jason Ebaugh
6/21/12 Gerry Flanagan
6/21/12 Richard Fateman
6/21/12 Chris Degnen
6/21/12 Bill Rowe
6/21/12 David Bailey
6/21/12 Christoph Lhotka
6/21/12 David Reiss
6/22/12 Vince Virgilio
6/22/12 Albert Retey