"It would be really really helpful to have a clearer idea of what you
are trying to do."
Amen!
But in R, "constructing" objects by extending them piece by piece is
generally very inefficient (e.g.
https://r-craft.org/growing-objects-and-loop-memory-pre-allocation/),
although sometimes?/often? unavoidable (hence the relevance of your
comment above). R generally prefers to take a "whole object" point of
view ( see R books by Chambers, et. al.) and provides code for basic
operations like vector/matrix, etc. construction to do so. When this
is not possible, I suspect "optimal" efficient strategies for
allocating space to build objects gets you into the weeds of how R
works.
Cheers,
Bert
On Sat, Mar 2, 2024 at 1:02?AM Richard O'Keefe <raoknz at gmail.com>
wrote:>
> The matrix equivalent of
> x <- ...
> v <- ...
> x[length(x)+1] <- v
> is
> m <- ...
> r <- ...
> m <- rbind(m, r)
> or
> m <- ...
> k <- ...
> m <- cbind(m, c)
>
> A vector or matrix so constructed never has "holes" in it.
> It's better to think of CONSTRUCTING vectors and matrices rather than
> INITIALISING them,
> because always being fully defined is important.
>
> It would be really really helpful to have a clearer idea of what you
> are trying to do.
>
> On Fri, 1 Mar 2024 at 03:31, Ebert,Timothy Aaron <tebert at ufl.edu>
wrote:
> >
> > You could declare a matrix much larger than you intend to use. This
works with a few megabytes of data. It is not very efficient, so scaling up may
become a problem.
> > m22 <- matrix(NA, 1:600000, ncol=6)
> >
> > It does not work to add a new column to the matrix, as in you get an
error if you try m22[ , 7] but convert to data frame and add a column
> >
> > m23 <- data.frame(m22)
> > m23$x7 <- 12
> >
> > The only penalty that I know of to having unused space in a matrix is
the amount of memory it takes. One side effect is that your program may have a
mistake that you would normally catch with a subscript out of bounds error but
with the extra space it now runs without errors.
> >
> > Tim
> >
> >
> >
> > -----Original Message-----
> > From: R-help <r-help-bounces at r-project.org> On Behalf Of
Richard O'Keefe
> > Sent: Thursday, February 29, 2024 5:29 AM
> > To: Steven Yen <styen at ntu.edu.tw>
> > Cc: R-help Mailing List <r-help at r-project.org>
> > Subject: Re: [R] Initializing vector and matrices
> >
> > [External Email]
> >
> > x <- numeric(0)
> > for (...) {
> > x[length(x)+1] <- ...
> > }
> > works.
> > You can build a matrix by building a vector one element at a time this
way, and then reshaping it at the end. That only works if you don't need it
to be a matrix at all times.
> > Another approach is to build a list of rows. It's not a matrix,
but a list of rows can be a *ragged* matrix with rows of varying length.
> >
> > On Wed, 28 Feb 2024 at 21:57, Steven Yen <styen at ntu.edu.tw>
wrote:
> > >
> > > Is there as way to initialize a vector (matrix) with an unknown
length
> > > (dimension)? NULL does not seem to work. The lines below work
with a
> > > vector of length 4 and a matrix of 4 x 4. What if I do not know
> > > initially the length/dimension of the vector/matrix?
> > >
> > > All I want is to add up (accumulate) the vector and matrix as I
go
> > > through the loop.
> > >
> > > Or, are there other ways to accumulate such vectors and matrices?
> > >
> > > > x<-rep(0,4) # this works but I like to leave the length
open >
> > > for (i in 1:3){
> > > + x1<-1:4
> > > + x<-x+x1
> > > + }
> > > > x
> > > [1] 3 6 9 12
> > >
> > > > y = 0*matrix(1:16, nrow = 4, ncol = 4); # this works but I
like to
> > > leave the dimension open
> > > [,1] [,2] [,3] [,4]
> > > [1,] 0 0 0 0
> > > [2,] 0 0 0 0
> > > [3,] 0 0 0 0
> > > [4,] 0 0 0 0
> > > > for (i in 1:3){
> > > + y1<-matrix(17:32, nrow = 4, ncol = 4)
> > > + y<-y+y1
> > > + }
> > > > y
> > > [,1] [,2] [,3] [,4]
> > > [1,] 51 63 75 87
> > > [2,] 54 66 78 90
> > > [3,] 57 69 81 93
> > > [4,] 60 72 84 96
> > > >
> > >
> > > ______________________________________________
> > > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more,
see
> > > https://stat/
> > >
.ethz.ch%2Fmailman%2Flistinfo%2Fr-help&data=05%7C02%7Ctebert%40ufl.edu
> > >
%7Cdbccaccf29674b10b17308dc39114d38%7C0d4da0f84a314d76ace60a62331e1b84
> > >
%7C0%7C0%7C638447993707432549%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAw
> > >
MDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata>
> > PtWjcDOnwO7PArVOSdgYbpz8ksjDPK%2Bn9ySyhwQC0gE%3D&reserved=0
> > > PLEASE do read the posting guide
> > > http://www.r/
> > >
-project.org%2Fposting-guide.html&data=05%7C02%7Ctebert%40ufl.edu%7Cdb
> > >
ccaccf29674b10b17308dc39114d38%7C0d4da0f84a314d76ace60a62331e1b84%7C0%
> > >
7C0%7C638447993707438911%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiL
> > >
CJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=Igb16
> > > CBYgG21HLEDH4I4gfjjFBa3KjDFK8yEZUmBo8s%3D&reserved=0
> > > 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.