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.
