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
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