R help - Mar 2007 - dataframe layout

Can someone remind me how to change the columns in df.a into a two column 
df.b that contains one column of data and another column of the original 
column headings as levels.

Example:
a=1:3
b=4:6
c=7:9
df.a=data.frame(a,b,c)

Should become in df.b:
dat   lev
1      a
2      a
3      a
4      b
5      b
6      b
7      c
8      c
9      c

Thanks.

On Wed, 2007-03-14 at 03:53 -0500, Robert Baer wrote:
> Can someone remind me how to change the columns in df.a into a two column 
> df.b that contains one column of data and another column of the original 
> column headings as levels.
> 
> Example:
> a=1:3
> b=4:6
> c=7:9
> df.a=data.frame(a,b,c)
> 
> Should become in df.b:
> dat   lev
> 1      a
> 2      a
> 3      a
> 4      b
> 5      b
> 6      b
> 7      c
> 8      c
> 9      c
> 
> Thanks.
One option is stack()
> a=1:3
> b=4:6
> c=7:9
> df.a=data.frame(a,b,c)
> df.a
  a b c
1 1 4 7
2 2 5 8
3 3 6 9
> stack(df.a)
  values ind
1      1   a
2      2   a
3      3   a
4      4   b
5      5   b
6      6   b
7      7   c
8      8   c
9      9   c
> class(stack(df.a))
[1] "data.frame"

HTH

G

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Robert Baer wrote:
> Can someone remind me how to change the columns in df.a into a two column 
> df.b that contains one column of data and another column of the original 
> column headings as levels.
> 
> Example:
> a=1:3
> b=4:6
> c=7:9
> df.a=data.frame(a,b,c)
> 
> Should become in df.b:
> dat   lev
> 1      a
> 2      a
> 3      a
> 4      b
> 5      b
> 6      b
> 7      c
> 8      c
> 9      c
  Here are a couple of different approaches:

df.b <- data.frame(dat = unlist(df.a),
                   lev = rep(names(df.a), each = dim(df.a)[1]))

df.b
   dat lev
a1   1   a
a2   2   a
a3   3   a
b1   4   b
b2   5   b
b3   6   b
c1   7   c
c2   8   c
c3   9   c

library(reshape)
melt(df.a, measure.var = names(df.a), variable_name = "lev")

  lev value
1   a     1
2   a     2
3   a     3
4   b     4
5   b     5
6   b     6
7   c     7
8   c     8
9   c     9
> Thanks.
> 
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