Oh, I get it. The context was in choosing columns to set to 0 via a **predicate**.
Sorry for the noise. Bert On Mon, Apr 25, 2022 at 7:39 AM Bert Gunter <bgunter.4...@gmail.com> wrote: > > Yes, sorry. But it's with the logical cast it's still M[, c(FALSE, > TRUE, FALSE)] which is M[, 2], and so I still don't get the point. > > Bert Gunter > > "The trouble with having an open mind is that people keep coming along > and sticking things into it." > -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) > > On Mon, Apr 25, 2022 at 7:33 AM Eric Berger <ericjber...@gmail.com> wrote: > > > > M[,x==1] is not the same as M[,x] :-) > > However, M[,!!x] is the same as M[,x==1] and saves one character! > > The point of this is "I can name that tune in ... " (as if that was not > > obvious) > > > > > > > > On Mon, Apr 25, 2022 at 5:30 PM Bert Gunter <bgunter.4...@gmail.com> wrote: > >> > >> x == 1 is the same as M[, x] so your expression is the same as > >> M[, c(FALSE, TRUE, FALSE)] <- 0 > >> which is the same as M[, 2] <- 0 > >> > >> So what is the point of all this, exactly? > >> > >> Bert > >> > >> On Mon, Apr 25, 2022 at 7:18 AM Ivan Calandra <ivan.calan...@rgzm.de> > >> wrote: > >> > > >> > Hi Uwe, > >> > > >> > If I understood the problem completely and building up on Tim's answer, > >> > this is even easier: > >> > M <- A <- matrix(1:9, ncol = 3) > >> > x <- c(0, 1, 0) > >> > M[, x == 1] <- 0 > >> > M > >> > > >> > The original issue was with the way ifelse works. The explanation is in > >> > the help page: "ifelse returns a value with the same shape as test||". > >> > So, because x[i] == 0 returns a single value (TRUE or FALSE), ifelse > >> > will also return a single value (either A[, i][1] or 0) and not a vector > >> > of length 3 as you wanted. This single value is recycled to fill M[, i], > >> > hence the result. > >> > > >> > HTH, > >> > Ivan > >> > > >> > -- > >> > Dr. Ivan Calandra > >> > Imaging lab > >> > RGZM - MONREPOS Archaeological Research Centre > >> > Schloss Monrepos > >> > 56567 Neuwied, Germany > >> > +49 (0) 2631 9772-243 > >> > https://www.researchgate.net/profile/Ivan_Calandra > >> > > >> > On 25/04/2022 16:01, Ebert,Timothy Aaron wrote: > >> > > A <- matrix(1:9,ncol=3) > >> > > x <- c(0,1,0) > >> > > M <- matrix(ncol=3,nrow=3) > >> > > M<-A > >> > > for(i in 1:3) { > >> > > if(x[i]){ > >> > > M[,i] <-0 > >> > > } > >> > > } > >> > > } > >> > > M > >> > > > >> > > The outcome you want is to set all of the middle column values to > >> > > zero. So I used x as a logical in an if test and when true everything > >> > > in that column is set to zero. > >> > > > >> > > Your approach also works but you must go through each element > >> > > explicitly. > >> > > A <- matrix(1:9,ncol=3) > >> > > x <- c(0,1,0) > >> > > M <- matrix(ncol=3,nrow=3) > >> > > for(j in 1:3){ > >> > > for(i in 1:3){ > >> > > ifelse(x[i]==1, M[j,i]<-0, M[j,i]<-A[j,i]) > >> > > } > >> > > } > >> > > M > >> > > > >> > > > >> > > > >> > > Tim > >> > > > >> > > -----Original Message----- > >> > > From: R-help <r-help-boun...@r-project.org> On Behalf Of Uwe Freier > >> > > Sent: Sunday, April 24, 2022 11:06 AM > >> > > To: r-help@r-project.org > >> > > Subject: [R] Confusing fori or ifelse result in matrix manipulation > >> > > > >> > > [External Email] > >> > > > >> > > Hello, > >> > > > >> > > sorry for the newbie question but I can't find out where I'm wrong. > >> > > > >> > > A <- matrix(1:9,ncol=3) > >> > > x <- c(0,1,0) > >> > > M <- matrix(ncol=3,nrow=3) > >> > > for(i in 1:3) { > >> > > M[,i] <- ifelse(x[i] == 0, A[,i], 0) > >> > > } > >> > > > >> > > expected: > >> > > > >> > >> M > >> > > [,1] [,2] [,3] > >> > > [1,] 1 0 7 > >> > > [2,] 2 0 8 > >> > > [3,] 3 0 9 > >> > > > >> > > > >> > > but the result is: > >> > > > >> > >> M > >> > > [,1] [,2] [,3] > >> > > [1,] 1 0 7 > >> > > [2,] 1 0 7 > >> > > [3,] 1 0 7 > >> > > > >> > > > >> > > If I do it "manually": > >> > > > >> > >> M[,1] <- A[,1] > >> > >> M[,2] <- 0 > >> > >> M[,3] <- A[,3] > >> > > M is as expected, where is my misconception? > >> > > > >> > > Thanks for any hint and best regards, > >> > > > >> > > Uwe > >> > > > >> > > ______________________________________________ > >> > > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > >> > > https://urldefense.proofpoint.com/v2/url?u=https-3A__stat.ethz.ch_mailman_listinfo_r-2Dhelp&d=DwICAg&c=sJ6xIWYx-zLMB3EPkvcnVg&r=9PEhQh2kVeAsRzsn7AkP-g&m=eyJm06tVDfKvtMDgz6oIWM-WVdoW3Szzb5G6rq0cCO_cB6ljj2x80E4oRkt3Vgba&s=K2RWPvtxaxwigGGH2oOrg8qiDWC5KTu60b8Wjybwsg4&e= > >> > > PLEASE do read the posting guide > >> > > https://urldefense.proofpoint.com/v2/url?u=http-3A__www.R-2Dproject.org_posting-2Dguide.html&d=DwICAg&c=sJ6xIWYx-zLMB3EPkvcnVg&r=9PEhQh2kVeAsRzsn7AkP-g&m=eyJm06tVDfKvtMDgz6oIWM-WVdoW3Szzb5G6rq0cCO_cB6ljj2x80E4oRkt3Vgba&s=L9VXAAYzIzrG2h17hBO-Qfg_EoS2mRQbjs3sRESp62Q&e= > >> > > and provide commented, minimal, self-contained, reproducible code. > >> > > > >> > > ______________________________________________ > >> > > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > >> > > 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. > >> > > >> > ______________________________________________ > >> > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > >> > 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. > >> > >> ______________________________________________ > >> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > >> 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. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
