[R] Reshape matrix from wide to long format

[Daren Tan]

I forgot the reshape equivalent for converting from wide to long format. Can someone help as my matrix is very big. The followin is just an example.

> m <- matrix(1:20, nrow=4, dimnames=list(LETTERS[1:4], letters[1:5]))
> m
a b c d e
A 1 5 9 13 17
B 2 6 10 14 18
C 3 7 11 15 19
D 4 8 12 16 20

> as.data.frame(cbind(rep(rownames(m), ncol(m)), rep(colnames(m), each=nrow(m)), c(m)))
V1 V2 V3
1 A a 1
2 B a 2
3 C a 3
4 D a 4
5 A b 5
6 B b 6
7 C b 7
8 D b 8
9 A c 9
10 B c 10
11 C c 11
12 D c 12
13 A d 13
14 B d 14
15 C d 15
16 D d 16
17 A e 17
18 B e 18
19 C e 19
20 D e 20

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[Gabor Grothendieck]

Try this:

> as.data.frame.table(m)
Var1 Var2 Freq

1 A a 1
2 B a 2
3 C a 3
4 D a 4
5 A b 5
6 B b 6
7 C b 7
8 D b 8
9 A c 9
10 B c 10
11 C c 11
12 D c 12
13 A d 13
14 B d 14
15 C d 15
16 D d 16
17 A e 17
18 B e 18
19 C e 19
20 D e 20

[stephen sefick]

#handy if you like ggplot2 as this is required
#I think this is what you want
library(reshape)

m <- matrix(1:20, nrow=4, dimnames=list(LETTERS[1:4], letters[1:5]))

melt(m)

--
Stephen Sefick

Let's not spend our time and resources thinking about things that are
so little or so large that all they really do for us is puff us up and
make us feel like gods. We are mammals, and have not exhausted the
annoying little problems of being mammals.

-K. Mullis

[Dieter Menne]

Daren Tan wrote:
>
>
> I forgot the reshape equivalent for converting from wide to long format.

> Can someone help as my matrix is very big. The following is just an

> example.
>
>> m <- matrix(1:20, nrow=4, dimnames=list(LETTERS[1:4], letters[1:5]))
>

Gabor's solution is uses more basic functions, but package reshape or
function reshape(...direction="long") would also work

library(reshape)

m <- matrix(1:20, nrow=4, dimnames=list(LETTERS[1:4], letters[1:5]))

mdf = cbind(V1=rownames(m),as.data.frame(m))
melt(mdf)

Dieter

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