On Jul 1, 2011, at 1:31 PM, Marc Jekel wrote:
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.:
?which.min # should have been linked from the help(which) page. ...
Yep, it is.
> mtx <- matrix(scan(textConnection("1 2 4
+ 4 5 3
+ 1 3 4")), 3, byrow=TRUE)
Read 9 items
> mtx
[,1] [,2] [,3]
[1,] 1 2 4
[2,] 4 5 3
[3,] 1 3 4
> apply(mtx, 2, which.min)
[1] 1 1 2
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: je...@coll.mpg.de
phone: ++49 (0) 228 91416-852
http://www.coll.mpg.de/team/page/marc_jekel-0
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