Converting a numeric matrix into a data.table (or data.frame)

Question

Hoping there\'s a simple answer here but I can\'t find it anywhere.

I have a numeric matrix with labelled rows and columns:

     1    2    3    4
a    6          


        

Answer 1

Use melt from reshape2:

library(reshape2)
#Fake data
x <- matrix(1:12, ncol = 3)
colnames(x) <- letters[1:3]
rownames(x) <- 1:4
x.m <- melt(x)
x.m

   Var1 Var2 value
1     1    a     1
2     2    a     2
3     3    a     3
4     4    a     4
...