R help - Dec 2009 - expand.grid applied to a matrix

Dear R gurus,
I'm looking for a way to expand a matrix to a data frame as detailed below:
given a Matrix M with attribute
dimnames=list(c("a","b"),c("u","v")),
return
a data frame df.M with
df.M$row   df.M$col   df.M$val
"a"            "u"           M["a","u"]
"b"            "v"           M["b". "v"]
"a"            "u"          M["a", "u"]
"b"            "v"           M["b", "v"]

expand.grid(M) almost does the job as it flattens M to a vector
but then the attribute dimnames gets lost.
I can always do merge(expand.grid(dimnames(M)), expand.grid(M), by=0)
but I'm wondering if there is a more concise way to do it.

Thanks for any help!

jc

	[[alternative HTML version deleted]]

On Tue, 15 Dec 2009, Jean-Christophe Domenge wrote:
> Dear R gurus,
> I'm looking for a way to expand a matrix to a data frame as detailed
below:
> given a Matrix M with attribute
dimnames=list(c("a","b"),c("u","v")),
return
> a data frame df.M with
> df.M$row   df.M$col   df.M$val
> "a"            "u"          
M["a","u"]
> "b"            "v"           M["b".
"v"]
> "a"            "u"          M["a",
"u"]
> "b"            "v"           M["b",
"v"]
>
Do you really want two copies of diag(M) only or is that a typo??

If a typo, try

 	df.M <- as.data.frame.table( M )
 	colnames( df.M ) <- c('row', 'col', 'val' )

If you want what your example shows, then add this line:

 	df.M <- df.M[ c( 1, 4, 1, 4 ), ]

HTH,

Chuck

> expand.grid(M) almost does the job as it flattens M to a vector
> but then the attribute dimnames gets lost.
> I can always do merge(expand.grid(dimnames(M)), expand.grid(M), by=0)
> but I'm wondering if there is a more concise way to do it.
>
> Thanks for any help!
>
> jc
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901