[R] how to apply several math/logic operations on columns/rows of a matrix

[Marc Jekel]

Dear R-Fans,

The more I work with matrices (e.g., data.frames) the more I think it 
would be helpful to have functions to apply (several!) mathematical 
and/or logical operators column- or row-wise in a matrix.

I know the function apply() and all its derivates (e.g., lapply)  but I 
think this does not help for solving  (e.g.) the following task:

assume there is a 3x3 matrix:

1    2    4
4    5    3
1    3    4

How do I find - for each column separately - the position of the 
column's minimum without using loop commands, i.e.:

I could extract each column in a loop and use something like:

for (loopColumn in 1 : 3){

extractedColumnVector  = myMatrix[, loopColumn]

position = which(extractedColumnVector == min (extractedColumnVector ) )

print(position)
}

I think that there should be something simpler out there to handle these 
kinds of tasks (maybe there is and I just don't know but I checked 
several R books and could not find a command to do this).

It would be great to have a function in which it is possible to define a 
sequence of commands that can be applied column/row-wise.

Thanks for a hint,

Marc

-- 
Dipl.-Psych. Marc Jekel

MPI for Research on Collective Goods
Kurt-Schumacher-Str. 10
D-53113 Bonn
Germany

email: jekel at coll.mpg.de
phone: ++49 (0) 228 91416-852

http://www.coll.mpg.de/team/page/marc_jekel-0