From: Thaden, John J <ThadenJohnJ_at_uams.edu>

Date: Sun 09 Jul 2006 - 13:45:57 EST

Dim = as.integer(c(5,5))))

*## 5 x 5 sparse Matrix of class "dgTMatrix"
*

*## [1,] 1 2 . . .
*

*## [2,] . . 7 . . <--- 7 = 3 + 4.
*

## [3,] . . . . .

*## [4,] . . . . .
*

*## [5,] . . . . 5
*

Dim = as.integer(c(5,5))))

*## 5 x 5 sparse Matrix of class "dgCMatrix"
*

*##
*

*## [1,] 1 2 . .
*

*## [2,] . . 4 . <-- the datum '3' has been lost.
*

## [3,] . . . .

*## [4,] . . . .
*

*## [5,] . . . 5
*

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Sun Jul 09 13:59:53 2006

Date: Sun 09 Jul 2006 - 13:45:57 EST

In the Matrix package v. 0.995-11 I see that the dgTMatrix
Class for compressed, sparse, triplet-form matrices handles
Identically indexed data instances by summing their values,
e.g.,

library(Matrix)

(Mt <- new("dgTMatrix",

i = as.integer(c(0,0,1,1,4)), j = as.integer(c(0,1,2,2,4)), x = as.double(1:5),

Dim = as.integer(c(5,5))))

## [3,] . . . . .

# If instead I make a dgCMatrix-class matrix, the first # instance is overwritten by the second, e.g.,

library(Matrix)

(Mc <- new("dgCMatrix",

i = as.integer(c(0,0,1,1,4)), p = as.integer(c(0,1,2,4,5)), x = as.double(1:5),

Dim = as.integer(c(5,5))))

## [3,] . . . .

# If one arrives at the dgCMatrix via the dgTMatrix class, # the summed value is of course preserved, e.g.,

(Mtc <- as(Mt, "dgCMatrix"))

*## 5 x 5 sparse Matrix of class "dgCMatrix"
**##
**## [1,] 1 2 . . .
*

## [2,] . . 7 . .

*## [3,] . . . . .
**## [4,] . . . . .
**## [5,] . . . . 5
*

As there is nothing inherent in either compressed, sparse, format that would prevent recognition and handling of duplicated index pairs, I'm curious why the dgCMatrix class doesn't also add x values in those instances? I wonder also if others might benefit also by being able to choose how these instances are handled, i.e., whether they are summed, averaged or overwritten?

-John Thaden, Ph.D.

Research Assistant Professor of Geriatrics
University of Arkansas for Medical Sciences
Little Rock AR, USA

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