Dear all,
I am pretty sure that this has been discussed before. Unfortunately, I
can not find anything in the archives -- probably because I am
"RSiteSearching" for the wrong terms. If I remember correctly, I think I
even asked this question a few years ago. But I cannot even find this.
The basic problem is that a result depends on a previous result. This is
easy with a loop--but how can I do this without a loop?
Lets give an example:
initial.matrix <- rbind(rep(1,4), matrix(0,ncol=4,nrow=5))
the.other.matrix <- matrix(runif(20), ncol=4, nrow=5)
the initial matrix should be filled according to the following
(pseudo-code) rule:
if (row==1) initial.matrix[1,] <- 1
if (row>1) initial.matrix[x,] <- initial.matrix[x-1,] *
the.other.matrix[x-1,]
as I said this is easy to do with a loop:
for (i in 2:(nrow(initial.matrix))) {
initial.matrix[i,] <- initial.matrix[i-1,]*the.other.matrix[i-1,]
}
initial.matrix
But how can I do this without a loop?
Thank you already in advance!
Roland
Result depends on previous result; easy with a loop; but without a loop?
3 messages · Roland Rau, Ravi Varadhan
Dear all,
in the meantime, I found a solution -- thank to a suggestion sent by
Mark Leeds to me off-list.
All the best,
Roland
set.seed(1234)
initial.matrix <- rbind(rep(1,4), matrix(0,ncol=4,nrow=5))
the.other.matrix <- matrix(runif(20), ncol=4, nrow=5)
for (i in 2:(nrow(initial.matrix))) {
initial.matrix[i,] <- initial.matrix[i-1,]*the.other.matrix[i-1,]
}
### that is how it should look like:
initial.matrix
### this is Mark's suggestion (if I understood it correctly)
initial.matrix2 <- rbind(rep(1,4), matrix(1,ncol=4,nrow=5))
initial.matrix2[-1,] <- sapply(1:ncol(initial.matrix2),
function(.col) {
cumprod(initial.matrix2[-(nrow(initial.matrix2)),.col]
* the.other.matrix[,.col])
}
)
## and it works!!!
initial.matrix2
if (all(initial.matrix==initial.matrix2)) cat("Good\n") else cat("Bad\n")
## yes, I know, such comparisons of floats are notoriously problematic
Roland Rau wrote:
Dear all,
I am pretty sure that this has been discussed before. Unfortunately, I
can not find anything in the archives -- probably because I am
"RSiteSearching" for the wrong terms. If I remember correctly, I think I
even asked this question a few years ago. But I cannot even find this.
The basic problem is that a result depends on a previous result. This is
easy with a loop--but how can I do this without a loop?
Lets give an example:
initial.matrix <- rbind(rep(1,4), matrix(0,ncol=4,nrow=5))
the.other.matrix <- matrix(runif(20), ncol=4, nrow=5)
the initial matrix should be filled according to the following
(pseudo-code) rule:
if (row==1) initial.matrix[1,] <- 1
if (row>1) initial.matrix[x,] <- initial.matrix[x-1,] *
the.other.matrix[x-1,]
as I said this is easy to do with a loop:
for (i in 2:(nrow(initial.matrix))) {
initial.matrix[i,] <- initial.matrix[i-1,]*the.other.matrix[i-1,]
}
initial.matrix
But how can I do this without a loop?
Thank you already in advance!
Roland
______________________________________________ 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.
Roland, You can test for the "sameness" of floating-point results as follows: all.equal(initial.matrix, initial.matrix2) By default, it uses a tolerance = .Machine$double.eps ^ 0.5 (roughly, 1.e-08). You can decrease this if you want a more stringent test for sameness. all.identical(initial.matrix, initial.matrix2) This tests for "identicality", which, of course, is not appropriate for floating point computations. Ravi. ---------------------------------------------------------------------------- ------- Ravi Varadhan, Ph.D. Assistant Professor, The Center on Aging and Health Division of Geriatric Medicine and Gerontology Johns Hopkins University Ph: (410) 502-2619 Fax: (410) 614-9625 Email: rvaradhan at jhmi.edu Webpage: http://www.jhsph.edu/agingandhealth/People/Faculty/Varadhan.html ---------------------------------------------------------------------------- -------- -----Original Message----- From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Roland Rau Sent: Friday, December 14, 2007 2:33 PM To: 'r-help at stat.math.ethz.ch' Subject: Re: [R] Result depends on previous result; easy with a loop; but without a loop? Dear all, in the meantime, I found a solution -- thank to a suggestion sent by Mark Leeds to me off-list. All the best, Roland set.seed(1234) initial.matrix <- rbind(rep(1,4), matrix(0,ncol=4,nrow=5)) the.other.matrix <- matrix(runif(20), ncol=4, nrow=5) for (i in 2:(nrow(initial.matrix))) { initial.matrix[i,] <- initial.matrix[i-1,]*the.other.matrix[i-1,] } ### that is how it should look like: initial.matrix ### this is Mark's suggestion (if I understood it correctly) initial.matrix2 <- rbind(rep(1,4), matrix(1,ncol=4,nrow=5)) initial.matrix2[-1,] <- sapply(1:ncol(initial.matrix2), function(.col) { cumprod(initial.matrix2[-(nrow(initial.matrix2)),.col] * the.other.matrix[,.col]) } ) ## and it works!!! initial.matrix2 if (all(initial.matrix==initial.matrix2)) cat("Good\n") else cat("Bad\n") ## yes, I know, such comparisons of floats are notoriously problematic
Roland Rau wrote:
Dear all,
I am pretty sure that this has been discussed before. Unfortunately, I
can not find anything in the archives -- probably because I am
"RSiteSearching" for the wrong terms. If I remember correctly, I think I
even asked this question a few years ago. But I cannot even find this.
The basic problem is that a result depends on a previous result. This is
easy with a loop--but how can I do this without a loop?
Lets give an example:
initial.matrix <- rbind(rep(1,4), matrix(0,ncol=4,nrow=5))
the.other.matrix <- matrix(runif(20), ncol=4, nrow=5)
the initial matrix should be filled according to the following
(pseudo-code) rule:
if (row==1) initial.matrix[1,] <- 1
if (row>1) initial.matrix[x,] <- initial.matrix[x-1,] *
the.other.matrix[x-1,]
as I said this is easy to do with a loop:
for (i in 2:(nrow(initial.matrix))) {
initial.matrix[i,] <- initial.matrix[i-1,]*the.other.matrix[i-1,]
}
initial.matrix
But how can I do this without a loop?
Thank you already in advance!
Roland
______________________________________________ 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.
______________________________________________ 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.