Converting from 0 and 1 to -1 and 1
in [General Programming]
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From: Ikke on 5 May 2010 04:30 Hi everybody, There's a function that basically returns an integer, either 0 or 1, but I'd like it to return -1 or 1. Obviously I can't alter the function itself, otherwise there wouldn't be a problem. The simplest solution would be to just check for the value with an if statement, like so: if function = 0 then value = -1 else value = 1 But I'd like to do it in one statement (don't ask why). Is there a way to convert both values (0 or 1) to -1 and 1 respectively, perhaps using some maths? I can't seem to find a way... Thanks in advance, Ikke! --- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
From: Jussi Piitulainen on 5 May 2010 04:43 Ikke writes: > There's a function that basically returns an integer, either 0 or 1, > but I'd like it to return -1 or 1. Obviously I can't alter the > function itself, otherwise there wouldn't be a problem. > > The simplest solution would be to just check for the value with an > if statement, like so: > if function = 0 then > value = -1 > else > value = 1 > > But I'd like to do it in one statement (don't ask why). Is there a > way to convert both values (0 or 1) to -1 and 1 respectively, > perhaps using some maths? I can't seem to find a way... Since 2*0 - 1 == -1 and 2*1 - 1 == 1, you can do simple arithmetic: value = 2*function - 1 Or if False is treated as 0 and True as 1, which I think they are but am too lazy to check, you can do the Iverson: value = (function == 1) - (function == 0)
From: Patricia Shanahan on 5 May 2010 04:45 Ikke wrote: > Hi everybody, > > There's a function that basically returns an integer, either 0 or 1, but > I'd like it to return -1 or 1. Obviously I can't alter the function itself, > otherwise there wouldn't be a problem. > > The simplest solution would be to just check for the value with an if > statement, like so: > if function = 0 then > value = -1 > else > value = 1 > > But I'd like to do it in one statement (don't ask why). Is there a way to > convert both values (0 or 1) to -1 and 1 respectively, perhaps using some > maths? I can't seem to find a way... value = 2 * function - 1 I got this by solving a couple of linear equations. In effect, you are asking for a function f such that f(0) is -1 and f(1) is 1. Given only two points, one of the possibilities for f is a straight line a*x+b through those points. Patricia
From: Jussi Piitulainen on 5 May 2010 04:46 Jussi Piitulainen writes: > Or if False is treated as 0 and True as 1, which I think they are > but am too lazy to check, you can do the Iverson: > > value = (function == 1) - (function == 0) Sorry, I thought I was in another newsgroup: it depends on the programming language whether that language treats truth values as 0 and 1.
From: Ikke on 5 May 2010 04:51
Jussi Piitulainen <jpiitula(a)ling.helsinki.fi> wrote in news:qotvdb2d9cm.fsf(a)ruuvi.it.helsinki.fi: > Jussi Piitulainen writes: > >> Or if False is treated as 0 and True as 1, which I think they are >> but am too lazy to check, you can do the Iverson: >> >> value = (function == 1) - (function == 0) > > Sorry, I thought I was in another newsgroup: it depends on the > programming language whether that language treats truth values > as 0 and 1. Never mind - your earlier suggested solution was perfect! Thanks, and thanks Patricia! Ikke --- news://freenews.netfront.net/ - complaints: news(a)netfront.net --- |