[R] Re: I want to pull out an element from each of a list of matrices

Prof Brian D Ripley ripley at stats.ox.ac.uk
Sat Oct 14 19:26:12 CEST 2000

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

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