Re: [R] odd feature
Gabor == Gabor Grothendieck [EMAIL PROTECTED] on Sun, 21 May 2006 09:47:07 -0400 writes: Gabor If you know that test is a scalar Gabor result - if (test) a else b Gabor will do it. Yes, indeed! IMO, ifelse(test, a, b) is much overused where as if(test) a else b is much UNDER used. From some e-mail postings, and even some documents (even printed books?), I get the impression that too many people think that ifelse(.,.,.) is to be used as expression / function and if(.) . else . only for program flow control. This leads to quite suboptimal code, and I personally use if(.) . else . __as expression__ much more frequently than ifelse(.,.,.) Martin Maechler, ETH Zurich. Gabor Here is another approach: Gabor as.vector(test * ts(a) + (!test) * ts(b)) Gabor On 5/21/06, ivo welch [EMAIL PROTECTED] wrote: Dear R wizards: I just got stung by the ifelse() feature. a - 10:15 b - 20:300 test - 1 ifelse(test,a,b) [1] 10 I had not realized that this was the default behavior---I had expected 10:15. mea culpa. however, I wonder whether it would make sense to replace ifelse with a different semantic, where if test is a single scalar, it means what a stupid user like me would imagine. Aside, I like the flexibility of R, but I am not thrilled by all the recycling rules. I either mean I want a scalar or a vector of equal/appropriate dimension. I never want a recycle of a smaller vector. (I do often use a recycle of a scalar.) regards, /iaw __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Gabor __ Gabor R-help@stat.math.ethz.ch mailing list Gabor https://stat.ethz.ch/mailman/listinfo/r-help Gabor PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
On 5/22/2006 3:26 AM, Martin Maechler wrote: Gabor == Gabor Grothendieck [EMAIL PROTECTED] on Sun, 21 May 2006 09:47:07 -0400 writes: Gabor If you know that test is a scalar Gabor result - if (test) a else b Gabor will do it. Yes, indeed! IMO, ifelse(test, a, b) is much overused where as if(test) a else b is much UNDER used. From some e-mail postings, and even some documents (even printed books?), I get the impression that too many people think that ifelse(.,.,.) is to be used as expression / function and if(.) . else . only for program flow control. This leads to quite suboptimal code, and I personally use if(.) . else . __as expression__ much more frequently than ifelse(.,.,.) For overuse of ifelse(), do you mean cases where test is length 1, so if() would work? Or are you thinking of something else? I'd also be interested in what you mean by quite suboptimal code. Are you thinking of things like if (test) temp - a else temp - b result - f(temp) versus result - f( if (test) a else b ) ? I would generally use the former, because it's easier to get the formatting right, and I find it easier to read. It's suboptimal in speed and memory use because of creating the temp variable, but in most cases I think that would be such a small difference that the small increase in readability is worthwhile. Duncan Murdoch Martin Maechler, ETH Zurich. Gabor Here is another approach: Gabor as.vector(test * ts(a) + (!test) * ts(b)) Gabor On 5/21/06, ivo welch [EMAIL PROTECTED] wrote: Dear R wizards: I just got stung by the ifelse() feature. a - 10:15 b - 20:300 test - 1 ifelse(test,a,b) [1] 10 I had not realized that this was the default behavior---I had expected 10:15. mea culpa. however, I wonder whether it would make sense to replace ifelse with a different semantic, where if test is a single scalar, it means what a stupid user like me would imagine. Aside, I like the flexibility of R, but I am not thrilled by all the recycling rules. I either mean I want a scalar or a vector of equal/appropriate dimension. I never want a recycle of a smaller vector. (I do often use a recycle of a scalar.) regards, /iaw __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Gabor __ Gabor R-help@stat.math.ethz.ch mailing list Gabor https://stat.ethz.ch/mailman/listinfo/r-help Gabor PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
Duncan Murdoch wrote: On 5/22/2006 3:26 AM, Martin Maechler wrote: Gabor == Gabor Grothendieck [EMAIL PROTECTED] on Sun, 21 May 2006 09:47:07 -0400 writes: Gabor If you know that test is a scalar Gabor result - if (test) a else b Gabor will do it. Yes, indeed! IMO, ifelse(test, a, b) is much overused where as if(test) a else b is much UNDER used. From some e-mail postings, and even some documents (even printed books?), I get the impression that too many people think that ifelse(.,.,.) is to be used as expression / function and if(.) . else . only for program flow control. This leads to quite suboptimal code, and I personally use if(.) . else . __as expression__ much more frequently than ifelse(.,.,.) For overuse of ifelse(), do you mean cases where test is length 1, so if() would work? Or are you thinking of something else? I'd also be interested in what you mean by quite suboptimal code. Are you thinking of things like if (test) temp - a else temp - b result - f(temp) versus result - f( if (test) a else b ) ? I would generally use the former, because it's easier to get the formatting right, and I find it easier to read. It's suboptimal in speed and memory use because of creating the temp variable, but in most cases I think that would be such a small difference that the small increase in readability is worthwhile. IMHO that approach too verbose and not more readable. Frank Duncan Murdoch Martin Maechler, ETH Zurich. Gabor Here is another approach: Gabor as.vector(test * ts(a) + (!test) * ts(b)) Gabor On 5/21/06, ivo welch [EMAIL PROTECTED] wrote: Dear R wizards: I just got stung by the ifelse() feature. a - 10:15 b - 20:300 test - 1 ifelse(test,a,b) [1] 10 I had not realized that this was the default behavior---I had expected 10:15. mea culpa. however, I wonder whether it would make sense to replace ifelse with a different semantic, where if test is a single scalar, it means what a stupid user like me would imagine. Aside, I like the flexibility of R, but I am not thrilled by all the recycling rules. I either mean I want a scalar or a vector of equal/appropriate dimension. I never want a recycle of a smaller vector. (I do often use a recycle of a scalar.) regards, /iaw __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html -- Frank E Harrell Jr Professor and Chair School of Medicine Department of Biostatistics Vanderbilt University __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
If you don't like f(if (temp) a else b) then what about temp - if (test) a else b f(temp) or temp - if (test) a else b f(temp) I think its easier to understand if you factor the temp- out since one immediately then knows the purpose of the statement is to set temp. On 5/22/06, Duncan Murdoch [EMAIL PROTECTED] wrote: On 5/22/2006 3:26 AM, Martin Maechler wrote: Gabor == Gabor Grothendieck [EMAIL PROTECTED] on Sun, 21 May 2006 09:47:07 -0400 writes: Gabor If you know that test is a scalar Gabor result - if (test) a else b Gabor will do it. Yes, indeed! IMO, ifelse(test, a, b) is much overused where as if(test) a else b is much UNDER used. From some e-mail postings, and even some documents (even printed books?), I get the impression that too many people think that ifelse(.,.,.) is to be used as expression / function and if(.) . else . only for program flow control. This leads to quite suboptimal code, and I personally use if(.) . else . __as expression__ much more frequently than ifelse(.,.,.) For overuse of ifelse(), do you mean cases where test is length 1, so if() would work? Or are you thinking of something else? I'd also be interested in what you mean by quite suboptimal code. Are you thinking of things like if (test) temp - a else temp - b result - f(temp) versus result - f( if (test) a else b ) ? I would generally use the former, because it's easier to get the formatting right, and I find it easier to read. It's suboptimal in speed and memory use because of creating the temp variable, but in most cases I think that would be such a small difference that the small increase in readability is worthwhile. Duncan Murdoch Martin Maechler, ETH Zurich. Gabor Here is another approach: Gabor as.vector(test * ts(a) + (!test) * ts(b)) Gabor On 5/21/06, ivo welch [EMAIL PROTECTED] wrote: Dear R wizards: I just got stung by the ifelse() feature. a - 10:15 b - 20:300 test - 1 ifelse(test,a,b) [1] 10 I had not realized that this was the default behavior---I had expected 10:15. mea culpa. however, I wonder whether it would make sense to replace ifelse with a different semantic, where if test is a single scalar, it means what a stupid user like me would imagine. Aside, I like the flexibility of R, but I am not thrilled by all the recycling rules. I either mean I want a scalar or a vector of equal/appropriate dimension. I never want a recycle of a smaller vector. (I do often use a recycle of a scalar.) regards, /iaw __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Gabor __ Gabor R-help@stat.math.ethz.ch mailing list Gabor https://stat.ethz.ch/mailman/listinfo/r-help Gabor PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
On 5/22/2006 9:38 AM, Frank E Harrell Jr wrote: Duncan Murdoch wrote: On 5/22/2006 3:26 AM, Martin Maechler wrote: Gabor == Gabor Grothendieck [EMAIL PROTECTED] on Sun, 21 May 2006 09:47:07 -0400 writes: Gabor If you know that test is a scalar Gabor result - if (test) a else b Gabor will do it. Yes, indeed! IMO, ifelse(test, a, b) is much overused where as if(test) a else b is much UNDER used. From some e-mail postings, and even some documents (even printed books?), I get the impression that too many people think that ifelse(.,.,.) is to be used as expression / function and if(.) . else . only for program flow control. This leads to quite suboptimal code, and I personally use if(.) . else . __as expression__ much more frequently than ifelse(.,.,.) For overuse of ifelse(), do you mean cases where test is length 1, so if() would work? Or are you thinking of something else? I'd also be interested in what you mean by quite suboptimal code. Are you thinking of things like if (test) temp - a else temp - b result - f(temp) versus result - f( if (test) a else b ) ? I would generally use the former, because it's easier to get the formatting right, and I find it easier to read. It's suboptimal in speed and memory use because of creating the temp variable, but in most cases I think that would be such a small difference that the small increase in readability is worthwhile. IMHO that approach too verbose and not more readable. IMO terse unreadable :-) Duncan Murdoch Frank Duncan Murdoch Martin Maechler, ETH Zurich. Gabor Here is another approach: Gabor as.vector(test * ts(a) + (!test) * ts(b)) Gabor On 5/21/06, ivo welch [EMAIL PROTECTED] wrote: Dear R wizards: I just got stung by the ifelse() feature. a - 10:15 b - 20:300 test - 1 ifelse(test,a,b) [1] 10 I had not realized that this was the default behavior---I had expected 10:15. mea culpa. however, I wonder whether it would make sense to replace ifelse with a different semantic, where if test is a single scalar, it means what a stupid user like me would imagine. Aside, I like the flexibility of R, but I am not thrilled by all the recycling rules. I either mean I want a scalar or a vector of equal/appropriate dimension. I never want a recycle of a smaller vector. (I do often use a recycle of a scalar.) regards, /iaw __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
Gabor == Gabor Grothendieck [EMAIL PROTECTED] on Mon, 22 May 2006 09:31:14 -0400 writes: Gabor If you don't like f(if (temp) a else b) Gabor then what about Gabor temp - if (test) a else b Gabor f(temp) Gabor or Gabor temp - if (test) Gabor a Gabor else Gabor b Gabor f(temp) Gabor I think its easier to understand if you factor the temp- out since Gabor one immediately then knows the purpose of the statement is Gabor to set temp. I strongly agree with Gabor on the above. But, to Duncan's question: Yes, indeed, my main point was that people use ifelse(test, a, b) also in cases where test is known to be of length one. BTW, the 2nd point about why I don't ``like'' ifelse() so much is on its help page: Both 'a' and 'b' are fully evaluated even though only one of the two values of a[i], b[i] are used in the result. Martin Gabor On 5/22/06, Duncan Murdoch [EMAIL PROTECTED] wrote: On 5/22/2006 3:26 AM, Martin Maechler wrote: Gabor == Gabor Grothendieck [EMAIL PROTECTED] on Sun, 21 May 2006 09:47:07 -0400 writes: Gabor If you know that test is a scalar Gabor result - if (test) a else b Gabor will do it. Yes, indeed! IMO, ifelse(test, a, b) is much overused where as if(test) a else b is much UNDER used. From some e-mail postings, and even some documents (even printed books?), I get the impression that too many people think that ifelse(.,.,.) is to be used as expression / function and if(.) . else . only for program flow control. This leads to quite suboptimal code, and I personally use if(.) . else . __as expression__ much more frequently than ifelse(.,.,.) For overuse of ifelse(), do you mean cases where test is length 1, so if() would work? Or are you thinking of something else? I'd also be interested in what you mean by quite suboptimal code. Are you thinking of things like if (test) temp - a else temp - b result - f(temp) versus result - f( if (test) a else b ) ? I would generally use the former, because it's easier to get the formatting right, and I find it easier to read. It's suboptimal in speed and memory use because of creating the temp variable, but in most cases I think that would be such a small difference that the small increase in readability is worthwhile. Duncan Murdoch Martin Maechler, ETH Zurich. Gabor Here is another approach: Gabor as.vector(test * ts(a) + (!test) * ts(b)) Gabor On 5/21/06, ivo welch [EMAIL PROTECTED] wrote: Dear R wizards: I just got stung by the ifelse() feature. a - 10:15 b - 20:300 test - 1 ifelse(test,a,b) [1] 10 I had not realized that this was the default behavior---I had expected 10:15. mea culpa. however, I wonder whether it would make sense to replace ifelse with a different semantic, where if test is a single scalar, it means what a stupid user like me would imagine. Aside, I like the flexibility of R, but I am not thrilled by all the recycling rules. I either mean I want a scalar or a vector of equal/appropriate dimension. I never want a recycle of a smaller vector. (I do often use a recycle of a scalar.) regards, /iaw __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Gabor __ Gabor R-help@stat.math.ethz.ch mailing list Gabor https://stat.ethz.ch/mailman/listinfo/r-help Gabor PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
Due to lazy evaluation, I don't think a and b are fully evaluated: ifelse(1, a - 1, b - 2) [1] 1 a [1] 1 b Error: object b not found On 5/22/06, Martin Maechler [EMAIL PROTECTED] wrote: Gabor == Gabor Grothendieck [EMAIL PROTECTED] on Mon, 22 May 2006 09:31:14 -0400 writes: Gabor If you don't like f(if (temp) a else b) Gabor then what about Gabor temp - if (test) a else b Gabor f(temp) Gabor or Gabor temp - if (test) Gabor a Gabor else Gabor b Gabor f(temp) Gabor I think its easier to understand if you factor the temp- out since Gabor one immediately then knows the purpose of the statement is Gabor to set temp. I strongly agree with Gabor on the above. But, to Duncan's question: Yes, indeed, my main point was that people use ifelse(test, a, b) also in cases where test is known to be of length one. BTW, the 2nd point about why I don't ``like'' ifelse() so much is on its help page: Both 'a' and 'b' are fully evaluated even though only one of the two values of a[i], b[i] are used in the result. Martin Gabor On 5/22/06, Duncan Murdoch [EMAIL PROTECTED] wrote: On 5/22/2006 3:26 AM, Martin Maechler wrote: Gabor == Gabor Grothendieck [EMAIL PROTECTED] on Sun, 21 May 2006 09:47:07 -0400 writes: Gabor If you know that test is a scalar Gabor result - if (test) a else b Gabor will do it. Yes, indeed! IMO, ifelse(test, a, b) is much overused where as if(test) a else b is much UNDER used. From some e-mail postings, and even some documents (even printed books?), I get the impression that too many people think that ifelse(.,.,.) is to be used as expression / function and if(.) . else . only for program flow control. This leads to quite suboptimal code, and I personally use if(.) . else . __as expression__ much more frequently than ifelse(.,.,.) For overuse of ifelse(), do you mean cases where test is length 1, so if() would work? Or are you thinking of something else? I'd also be interested in what you mean by quite suboptimal code. Are you thinking of things like if (test) temp - a else temp - b result - f(temp) versus result - f( if (test) a else b ) ? I would generally use the former, because it's easier to get the formatting right, and I find it easier to read. It's suboptimal in speed and memory use because of creating the temp variable, but in most cases I think that would be such a small difference that the small increase in readability is worthwhile. Duncan Murdoch Martin Maechler, ETH Zurich. Gabor Here is another approach: Gabor as.vector(test * ts(a) + (!test) * ts(b)) Gabor On 5/21/06, ivo welch [EMAIL PROTECTED] wrote: Dear R wizards: I just got stung by the ifelse() feature. a - 10:15 b - 20:300 test - 1 ifelse(test,a,b) [1] 10 I had not realized that this was the default behavior---I had expected 10:15. mea culpa. however, I wonder whether it would make sense to replace ifelse with a different semantic, where if test is a single scalar, it means what a stupid user like me would imagine. Aside, I like the flexibility of R, but I am not thrilled by all the recycling rules. I either mean I want a scalar or a vector of equal/appropriate dimension. I never want a recycle of a smaller vector. (I do often use a recycle of a scalar.) regards, /iaw __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Gabor __ Gabor R-help@stat.math.ethz.ch mailing list Gabor https://stat.ethz.ch/mailman/listinfo/r-help Gabor PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
On Mon, 22 May 2006, Gabor Grothendieck wrote: Due to lazy evaluation, I don't think a and b are fully evaluated: ifelse(1, a - 1, b - 2) [1] 1 a [1] 1 b Error: object b not found yes. If you look at the code for ifelse() it evaluates the second argument if any test values are TRUE and the third argument if any test values are FALSE, so in the scalar case it does not evaluate both arguments. -thomas Thomas Lumley Assoc. Professor, Biostatistics [EMAIL PROTECTED] University of Washington, Seattle __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
On Sun, 21 May 2006, ivo welch wrote: Aside, I like the flexibility of R, but I am not thrilled by all the recycling rules. I either mean I want a scalar or a vector of equal/appropriate dimension. I never want a recycle of a smaller vector. (I do often use a recycle of a scalar.) One case where the vector-vector recycling rules are used is in vector-matrix operations: a-1:4 b-diag(4) a+b -thomas __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
TL == Thomas Lumley [EMAIL PROTECTED] on Mon, 22 May 2006 07:09:09 -0700 (PDT) writes: TL On Mon, 22 May 2006, Gabor Grothendieck wrote: Due to lazy evaluation, I don't think a and b are fully evaluated: ifelse(1, a - 1, b - 2) [1] 1 a [1] 1 b Error: object b not found TL yes. If you look at the code for ifelse() it evaluates TL the second argument if any test values are TRUE and the TL third argument if any test values are FALSE, so in the TL scalar case it does not evaluate both arguments. yes. And (Gabor), if you recall what I said earlier, it's pretty clear that I would not even *consider* using ifelse() in the scalar case. So my original statement was about the case ifelse() is designed for: The non-trivial vector case, and there my statement of fully evaluated does apply. Martin __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
On 5/22/06, Martin Maechler [EMAIL PROTECTED] wrote: TL == Thomas Lumley [EMAIL PROTECTED] on Mon, 22 May 2006 07:09:09 -0700 (PDT) writes: TL On Mon, 22 May 2006, Gabor Grothendieck wrote: Due to lazy evaluation, I don't think a and b are fully evaluated: ifelse(1, a - 1, b - 2) [1] 1 a [1] 1 b Error: object b not found TL yes. If you look at the code for ifelse() it evaluates TL the second argument if any test values are TRUE and the TL third argument if any test values are FALSE, so in the TL scalar case it does not evaluate both arguments. yes. And (Gabor), if you recall what I said earlier, it's pretty clear that I would not even *consider* using ifelse() in the scalar case. So my original statement was about the case ifelse() is designed for: The non-trivial vector case, and there my statement of fully evaluated does apply. Martin I don't think they are fully evaluated in the vector case either: ifelse(rep(TRUE,4), a - 1:4, b - 1:4) [1] 1 2 3 4 a [1] 1 2 3 4 b Error: object b not found __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
Gabor Grothendieck wrote: On 5/22/06, Martin Maechler [EMAIL PROTECTED] wrote: TL == Thomas Lumley [EMAIL PROTECTED] on Mon, 22 May 2006 07:09:09 -0700 (PDT) writes: TL On Mon, 22 May 2006, Gabor Grothendieck wrote: Due to lazy evaluation, I don't think a and b are fully evaluated: ifelse(1, a - 1, b - 2) [1] 1 a [1] 1 b Error: object b not found TL yes. If you look at the code for ifelse() it evaluates TL the second argument if any test values are TRUE and the TL third argument if any test values are FALSE, so in the TL scalar case it does not evaluate both arguments. yes. And (Gabor), if you recall what I said earlier, it's pretty clear that I would not even *consider* using ifelse() in the scalar case. So my original statement was about the case ifelse() is designed for: The non-trivial vector case, and there my statement of fully evaluated does apply. Martin I don't think they are fully evaluated in the vector case either: ifelse(rep(TRUE,4), a - 1:4, b - 1:4) [1] 1 2 3 4 a [1] 1 2 3 4 b Error: object b not found Martin's non-trivial means not all conditions are TRUE or not all are FALSE, then both statements are FULLY evaluated and he is right. See the ifelse() code which is not that hard to read... Uwe __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
Gabor == Gabor Grothendieck [EMAIL PROTECTED] on Mon, 22 May 2006 11:34:09 -0400 writes: Gabor On 5/22/06, Martin Maechler [EMAIL PROTECTED] wrote: TL == Thomas Lumley [EMAIL PROTECTED] on Mon, 22 May 2006 07:09:09 -0700 (PDT) writes: TL On Mon, 22 May 2006, Gabor Grothendieck wrote: Due to lazy evaluation, I don't think a and b are fully evaluated: ifelse(1, a - 1, b - 2) [1] 1 a [1] 1 b Error: object b not found TL yes. If you look at the code for ifelse() it evaluates TL the second argument if any test values are TRUE and the TL third argument if any test values are FALSE, so in the TL scalar case it does not evaluate both arguments. yes. And (Gabor), if you recall what I said earlier, it's pretty clear that I would not even *consider* using ifelse() in the scalar case. So my original statement was about the case ifelse() is designed for: The non-trivial vector case, and there my statement of fully evaluated does apply. Martin Gabor I don't think they are fully evaluated in the vector case either: ifelse(rep(TRUE,4), a - 1:4, b - 1:4) Gabor [1] 1 2 3 4 a Gabor [1] 1 2 3 4 b Gabor Error: object b not found PLEASE -- I said non-trivial above Martin __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
Hi Thomas: One case where the vector-vector recycling rules are used is in vector-matrix operations: a-1:4 b-diag(4) a+b is this last expression intended to be intuitive and thus desirable? if anything else, I would end up writing something like this more as an error than by intent. I would suggest that recycling might be better to be explicitly asked for by the user---though I am not sure what the syntax should be. allow.recycle(a+b) at the end, I think implicit recycling is a tradeoff between convenience and unintended errors. I would judge the convenience of implicit recycling to be fairly low, and the unintended error rate [with difficulty finding it] to be fairly high. I guess the R language has few options() that control its behavior---e.g., ala use strict; in perl. If it did, I would love to turn off implicit recycling, provided there is an explicit recycle possibility. I would not mind having the ability to be forced to define variables first, either, though this is not a big deal. R is pretty good in telling me when I use variables that have not been defined. regards, /ivo -thomas __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
On 5/22/2006 5:01 PM, ivo welch wrote: Hi Thomas: One case where the vector-vector recycling rules are used is in vector-matrix operations: a-1:4 b-diag(4) a+b is this last expression intended to be intuitive and thus desirable? if anything else, I would end up writing something like this more as an error than by intent. I would suggest that recycling might be better to be explicitly asked for by the user---though I am not sure what the syntax should be. allow.recycle(a+b) at the end, I think implicit recycling is a tradeoff between convenience and unintended errors. I would judge the convenience of implicit recycling to be fairly low, and the unintended error rate [with difficulty finding it] to be fairly high. I guess the R language has few options() that control its behavior---e.g., ala use strict; in perl. If it did, I would love to turn off implicit recycling, provided there is an explicit recycle possibility. While I agree with you about these things in principle, this is a very old S design decision, and I think it can't really change now. It would have to be a local change (i.e. in my namespace, do things strictly), and that's very unlikely to happen. I would not mind having the ability to be forced to define variables first, either, though this is not a big deal. R is pretty good in telling me when I use variables that have not been defined. There are some code tools around that help to detect such things. Duncan Murdoch __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
[R] odd feature
Dear R wizards: I just got stung by the ifelse() feature. a - 10:15 b - 20:300 test - 1 ifelse(test,a,b) [1] 10 I had not realized that this was the default behavior---I had expected 10:15. mea culpa. however, I wonder whether it would make sense to replace ifelse with a different semantic, where if test is a single scalar, it means what a stupid user like me would imagine. Aside, I like the flexibility of R, but I am not thrilled by all the recycling rules. I either mean I want a scalar or a vector of equal/appropriate dimension. I never want a recycle of a smaller vector. (I do often use a recycle of a scalar.) regards, /iaw __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
If you know that test is a scalar result - if (test) a else b will do it. Here is another approach: as.vector(test * ts(a) + (!test) * ts(b)) On 5/21/06, ivo welch [EMAIL PROTECTED] wrote: Dear R wizards: I just got stung by the ifelse() feature. a - 10:15 b - 20:300 test - 1 ifelse(test,a,b) [1] 10 I had not realized that this was the default behavior---I had expected 10:15. mea culpa. however, I wonder whether it would make sense to replace ifelse with a different semantic, where if test is a single scalar, it means what a stupid user like me would imagine. Aside, I like the flexibility of R, but I am not thrilled by all the recycling rules. I either mean I want a scalar or a vector of equal/appropriate dimension. I never want a recycle of a smaller vector. (I do often use a recycle of a scalar.) regards, /iaw __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] odd feature
ivo welch wrote: Dear R wizards: I just got stung by the ifelse() feature. a - 10:15 b - 20:300 test - 1 ifelse(test,a,b) [1] 10 I had not realized that this was the default behavior---I had expected 10:15. mea culpa. however, I wonder whether it would make sense to replace ifelse with a different semantic, where if test is a single scalar, it means what a stupid user like me would imagine. Aside, I like the flexibility of R, but I am not thrilled by all the recycling rules. I either mean I want a scalar or a vector of equal/appropriate dimension. I never want a recycle of a smaller vector. (I do often use a recycle of a scalar.) regards, /iaw The current behavior is logical to me. Are you looking for if(test) a else b? Frank -- Frank E Harrell Jr Professor and Chair School of Medicine Department of Biostatistics Vanderbilt University __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
