Hi, Can anyone explain what is going on...!? For a vector "x=seq(min,max,0.01)", when generating sub-vector "a" based on a starting value "st", things go as expected as long as "st" is not too close to the beginning of "x". For example, if x starts at -5 and increments by 0.01, whenever I try to generate the sub-vector "a" (as below) with a starting value of 0.49 or less it does not generate the expected output: The initial value of "a" is wrong. Thanks in advance for any clarity you can shed. Gary ...(please see two versions of code below).... #THIS WORKS...(st > -4.9) min = -5; max = 1; x=seq(min,max,0.01) st= -4.8 ; end= 0 a=x[((st-min)/0.01+1):((end-min)/0.01+1)] n=(st-min)/0.01+1 #compare a[1:10]; c(x[n:(n+9)]) #test... n x[1:n]; x[n] ### x[n]== x[1:n][n] ; As expected ########################################################## # BUT THIS IS WEIRD!!...(st <= -4.9) st= -4.90 ; end= 0 ### -> BUG in generation of a!! a=x[((st-min)/0.01+1):((end-min)/0.01+1)]; n=(st-min)/0.01+1 #compare a[1:10]; c(x[n:(n+9)]) #test n x[1:n]; x[n] ### NOW x[n] != x[1:n][n] !!?? What is going on!? -- View this message in context: http://r.789695.n4.nabble.com/Strange-subvector-output-x-n-x-1-n-n-tp4682526.html Sent from the R help mailing list archive at Nabble.com.
Strange subvector output --> x[n] != x[1:n][n]
3 messages · Gewart, Jeff Newmiller, Patrick Burns
Sigh. Google couldn't help you?
Try FAQ 7.31 and then use non-fractions to generate sequences... scale as desired. This is not unique to R.
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Gewart <gewart at biotron.com.au> wrote:
Hi, Can anyone explain what is going on...!? For a vector "x=seq(min,max,0.01)", when generating sub-vector "a" based on a starting value "st", things go as expected as long as "st" is not too close to the beginning of "x". For example, if x starts at -5 and increments by 0.01, whenever I try to generate the sub-vector "a" (as below) with a starting value of 0.49 or less it does not generate the expected output: The initial value of "a" is wrong. Thanks in advance for any clarity you can shed. Gary ...(please see two versions of code below).... #THIS WORKS...(st > -4.9) min = -5; max = 1; x=seq(min,max,0.01) st= -4.8 ; end= 0 a=x[((st-min)/0.01+1):((end-min)/0.01+1)] n=(st-min)/0.01+1 #compare a[1:10]; c(x[n:(n+9)]) #test... n x[1:n]; x[n] ### x[n]== x[1:n][n] ; As expected ########################################################## # BUT THIS IS WEIRD!!...(st <= -4.9) st= -4.90 ; end= 0 ### -> BUG in generation of a!! a=x[((st-min)/0.01+1):((end-min)/0.01+1)]; n=(st-min)/0.01+1 #compare a[1:10]; c(x[n:(n+9)]) #test n x[1:n]; x[n] ### NOW x[n] != x[1:n][n] !!?? What is going on!? -- View this message in context: http://r.789695.n4.nabble.com/Strange-subvector-output-x-n-x-1-n-n-tp4682526.html Sent from the R help mailing list archive at Nabble.com.
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
You've found an interesting corner of Circle 1 of 'The R Inferno'. http://www.burns-stat.com/documents/books/the-r-inferno/ The issue is that your 'n' in the final case is slightly less than 11. So: > n [1] 11 > as.integer(n) [1] 10 > 1:n [1] 1 2 3 4 5 6 7 8 9 10 11 The mystery to me is why `:` thinks it is doing an integer sequence but ends in 11 rather than 10. Most people are likely to think the mystery is why as.integer(n) is 10. The reason is that coercion to integer is truncation (except if the number is really close to the integer farther from 0). Why that and not round? Well, just because. (Actually probably speed back in the day when it could matter.) Pat
On 20/12/2013 04:33, Gewart wrote:
Hi, Can anyone explain what is going on...!? For a vector "x=seq(min,max,0.01)", when generating sub-vector "a" based on a starting value "st", things go as expected as long as "st" is not too close to the beginning of "x". For example, if x starts at -5 and increments by 0.01, whenever I try to generate the sub-vector "a" (as below) with a starting value of 0.49 or less it does not generate the expected output: The initial value of "a" is wrong. Thanks in advance for any clarity you can shed. Gary ...(please see two versions of code below).... #THIS WORKS...(st > -4.9) min = -5; max = 1; x=seq(min,max,0.01) st= -4.8 ; end= 0 a=x[((st-min)/0.01+1):((end-min)/0.01+1)] n=(st-min)/0.01+1 #compare a[1:10]; c(x[n:(n+9)]) #test... n x[1:n]; x[n] ### x[n]== x[1:n][n] ; As expected ########################################################## # BUT THIS IS WEIRD!!...(st <= -4.9) st= -4.90 ; end= 0 ### -> BUG in generation of a!! a=x[((st-min)/0.01+1):((end-min)/0.01+1)]; n=(st-min)/0.01+1 #compare a[1:10]; c(x[n:(n+9)]) #test n x[1:n]; x[n] ### NOW x[n] != x[1:n][n] !!?? What is going on!? -- View this message in context: http://r.789695.n4.nabble.com/Strange-subvector-output-x-n-x-1-n-n-tp4682526.html Sent from the R help mailing list archive at Nabble.com.
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Patrick Burns pburns at pburns.seanet.com twitter: @burnsstat @portfolioprobe http://www.portfolioprobe.com/blog http://www.burns-stat.com (home of: 'Impatient R' 'The R Inferno' 'Tao Te Programming')