R help - Oct 2000 - No subject

On Sat, 14 Oct 2000, niels Waller wrote:
> Dear colleagues,
> 
> I suspect there is a simple answer to this question -- but I cannot find
it.
> 
> Suppose I have a list of matrices.  I want to pull out an element (such as
> row 1, col 2) from each matrix.  Do I need a loop to do this? Or is there
an
> easy way to index this?
> 
> Let Z denote the list of matrices.  All matrices have the same order.  I
> want something like
>   Z[[.]][1,2]     (which of course will not work, but you get the idea)
lapply(Z, function(x) x[1,2])

should do this, giving a list.  Use sapply if you want a vector.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

On Sat, 14 Oct 2000, niels Waller wrote:
> 
> 
> 
> Dear colleagues,
> 
> I suspect there is a simple answer to this question -- but I cannot find
it.
> 
> Suppose I have a list of matrices.  I want to pull out an element (such as
> row 1, col 2) from each matrix.  Do I need a loop to do this? Or is there
an
> easy way to index this?
> 
> Let Z denote the list of matrices.  All matrices have the same order.  I
> want something like
>   Z[[.]][1,2]     (which of course will not work, but you get the idea)
> 
  lapply(Z,function(zi) zi[1,2])

will work. You may want to wrap this in unlist() to get a vector instead
of a list.

	-thomas

Thomas Lumley
Assistant Professor, Biostatistics
University of Washington, Seattle

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

Dear colleagues,

I suspect there is a simple answer to this question -- but I cannot find it.

Suppose I have a list of matrices.  I want to pull out an element (such as
row 1, col 2) from each matrix.  Do I need a loop to do this? Or is there an
easy way to index this?

Let Z denote the list of matrices.  All matrices have the same order.  I
want something like
  Z[[.]][1,2]     (which of course will not work, but you get the idea)


Thanks for any and all tips,

Niels Waller
Professor of Quantitative Methods and Evaluation
Department of Psychology and Human Development
Vanderbilt University

niels.waller at vanderbilt.edu

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._