Convert columns to rows keeping the name of the column

Question

Is there any way in R to Convert columns to rows keeping the name of the column?

Example input:

A   B
1   1
2   3
3   4
44  5

Output

 Group Number
  A       1
  A       2
  A       3
  A       44 
  B       1
  B       3
  B       4
  B       5

Answer 1

No need to use reshape2, you can use the stack function from base-R :

With your.data as your example:

res <- stack(your.data)
colnames(res) = c("Number", "Group")

gives you

> res
  Number Group
1      1     A
2      2     A
3      3     A
4     44     A
5      1     B
6      3     B
7      4     B
8      5     B

See also here.

---

Benchmarking melt from reshape2 and stack from base on bigger data:

require(reshape2)
set.seed(45)
DF <- data.frame(matrix(sample(20, 1e6, TRUE), ncol=100))

require(microbenchmark)
microbenchmark(stack(DF), melt(DF), times=100)

Unit: milliseconds
      expr      min       lq   median       uq      max neval
 stack(DF) 157.7084 187.1993 241.8206 251.7132 334.5488   100
  melt(DF) 174.6079 253.1088 261.6234 273.3971 443.9953   100

Seems like stack is faster, but by a margin of 20 milliseconds...