Re: Please post: Mathematica -another For loop problem
- To: mathgroup at smc.vnet.net
- Subject: [mg65768] Re: Please post: Mathematica -another For loop problem
- From: "Ray Koopman" <koopman at sfu.ca>
- Date: Mon, 17 Apr 2006 02:28:05 -0400 (EDT)
- References: <e1suc9$c7k$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
1.156 wrote: > [This post has been delayed due to email problems - moderator] > > I've got to manipulate some signed 12bit integer numbers from a file and > apparently Mathematica only handles 8 and 16 bit signed numbers > (probably for a very good reason). So I bring them in as 16 bits (and > they're stored that way with a leading zero nibble) and then I have to > do the following to make sense of them. I really don't know why this > code works but it does. > > For[i = 1, i < Length[y], i++, If[y[[i]] > 2048, y[[i]] = > y[[i]] - 2048, y[[i]] = y[[i]] + 2048]]; > > So to my question: once again I had to resort to a For loop to pull this > off and I know this is a no-no. But I'm so clueless about Mathematica > that I've never come up with a more sophisticated method after a year or > so of thinking about it. Can someone help (as they usually can)? > > Thanks, Rob hex from to 000 0 0 001 0 1 : : : 7ff 2047 2047 800 2048 -2048 801 2049 -2047 : : : ffe 4094 -2 fff 4095 -1 z = Map[If[# < 2048, #, #-4096]&, y] will do what you want. Note that Map returns a whole new vector that can be called whatever you want. y is not automatically overwritten. The equivalent short form is z = If[# < 2048, #, #-4096]& /@ y