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

[Bill Venables]

At 18:26 14/10/00 +0100, Prof Brian D Ripley wrote:
>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])

or

	lapply(Z, "[", 1, 2)

if you want to use the extractor function directly.  unlist() the result
for a vector of results.

>
>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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--
Bill Venables, Statistician                         Tel. +61 7 3826 7251 
CSIRO Marine Laboratories,                          Fax. +61 7 3826 7304
Cleveland, Qld, 4163                  Email: Bill.Venables at cmis.csiro.au
AUSTRALIA                        http://www.cmis.csiro.au/bill.venables/


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