Ivan Calandra
2022-Apr-25 14:18 UTC
[R] Confusing fori or ifelse result in matrix manipulation
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-bounces at r-project.org> On Behalf Of Uwe Freier > Sent: Sunday, April 24, 2022 11:06 AM > To: r-help at 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 at 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 at 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.
Bert Gunter
2022-Apr-25 14:30 UTC
[R] Confusing fori or ifelse result in matrix manipulation
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.calandra at 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-bounces at r-project.org> On Behalf Of Uwe Freier > > Sent: Sunday, April 24, 2022 11:06 AM > > To: r-help at 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 at 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 at 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 at 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.