Arrange elements on a matrix according to rowSums + short 'apply' Q

Greetings,

My goal is to create a Markov transition matrix (probability of moving from
one state to another) with the 'highest traffic' portion of the matrix
occupying the top-left section. Consider the following sample:

inputData<- c(
     c(5, 3, 1, 6, 7),
     c(9, 7, 3, 10, 11),
     c(1, 2, 3, 4, 5),
     c(2, 4, 6, 8, 10),
     c(9, 5, 2, 1, 1)
     )

MAT<- matrix(inputData, nrow = 5, ncol = 5, byrow = TRUE)
colnames(MAT)<- c("A", "B", "C", "D", "E")
rownames(MAT)<- c("A", "B", "C", "D", "E")

rowSums(MAT)

I wan to re-arrange the elements of this matrix such that the elements with
the largest row sums are placed to the top-left, in descending order. Does
this make sense? In this case the order I'm looking for would be B, D, A, E,
C Any thoughts?

As an aside, here is the function I've written to construct the transition
matrix. Is there a more elegant way to do this that doesn't involve a double
transpose?

TMAT<- apply(t(MAT), 2, function(X) X/sum(X))
TMAT<- t(TMAT)

I tried the following:

TMAT<- apply(MAT, 1, function(X) X/sum(X))

But my the custom function is still getting applied over the columns of the
array, rather than the rows. For a check try:

rowSums(TMAT)
colSums(TMAT)

Row sums here should equal 1...

Many thanks in advance,
Aaron

	[[alternative HTML version deleted]]

Hi,

Here is a not so easy way to do your first step, but it works:
MAT2 <- cbind(MAT, rowSums(MAT))
MAT[order(MAT2[,6], decreasing=TRUE),]

For the second, I don't know!

HTH,
Ivan


Le 12/2/2010 09:46, Aaron Polhamus a ?crit :

Greetings,

My goal is to create a Markov transition matrix (probability of moving
from
one state to another) with the 'highest traffic' portion of the matrix
occupying the top-left section. Consider the following sample:

inputData<- c(
? ? c(5, 3, 1, 6, 7),
? ? c(9, 7, 3, 10, 11),
? ? c(1, 2, 3, 4, 5),
? ? c(2, 4, 6, 8, 10),
? ? c(9, 5, 2, 1, 1)
? ? )

MAT<- matrix(inputData, nrow = 5, ncol = 5, byrow = TRUE)
colnames(MAT)<- c("A", "B", "C", "D", "E")
rownames(MAT)<- c("A", "B", "C", "D", "E")

rowSums(MAT)

I wan to re-arrange the elements of this matrix such that the elements
with
the largest row sums are placed to the top-left, in descending order. Does
this make sense? In this case the order I'm looking for would be B, D, A,
E,
C Any thoughts?

As an aside, here is the function I've written to construct the transition
matrix. Is there a more elegant way to do this that doesn't involve a
double
transpose?

TMAT<- apply(t(MAT), 2, function(X) X/sum(X))
TMAT<- t(TMAT)

I tried the following:

TMAT<- apply(MAT, 1, function(X) X/sum(X))

But my the custom function is still getting applied over the columns of
the
array, rather than the rows. For a check try:

rowSums(TMAT)
colSums(TMAT)

Row sums here should equal 1...

Many thanks in advance,
Aaron

? ? ? ?[[alternative HTML version deleted]]

--
Ivan CALANDRA
PhD Student
University of Hamburg
Biozentrum Grindel und Zoologisches Museum
Abt. S?ugetiere
Martin-Luther-King-Platz 3
D-20146 Hamburg, GERMANY
+49(0)40 42838 6231
ivan.calandra at uni-hamburg.de

**********
http://www.for771.uni-bonn.de
http://webapp5.rrz.uni-hamburg.de/mammals/eng/1525_8_1.php

Many thanks for the tips, those solved my queries. Still interested in how
to force custom functions to work over rows rather than columns when using
apply,