[R] from matrix to data.frame

Antje niederlein-rstat at yahoo.de
Tue Jan 20 16:04:07 CET 2009


Wow, there are a lot of possibilities... thank you all very much!!!
I guess, I'll go for "as.data.frame.table", because it's one line and does 
exactly what I want :-)

Ciao,
Antje



Antje schrieb:
> Hello,
> 
> I have a question how to reshape a given matrix to a data frame.
> 
> # ----------------------------------
>  > a <- matrix(1:25, nrow=5)
>  > a
>      [,1] [,2] [,3] [,4] [,5]
> [1,]    1    6   11   16   21
> [2,]    2    7   12   17   22
> [3,]    3    8   13   18   23
> [4,]    4    9   14   19   24
> [5,]    5   10   15   20   25
> 
>  > colnames(a) <- LETTERS[1:5]
>  > rownames(a) <- as.character(1:5)
>  > a
>   A  B  C  D  E
> 1 1  6 11 16 21
> 2 2  7 12 17 22
> 3 3  8 13 18 23
> 4 4  9 14 19 24
> 5 5 10 15 20 25
> 
> # -----------------------------------
> 
> This is an example on how my matrix looks like.
> Now, I'd like to reshape the data that I get a data frame with three 
> columns:
> 
> - the row name of the enty (X1)
> - the column name of the entry (X2)
> - the entry itself (X3)
> 
> like:
> 
> X1    X2    X3
> 1    A    1
> 2    A    2
> 3    A    3
> ....
> 1    B    6
> 2    B    7
> ....
> 5    E    25
> 
> How would you solve this problem in an elegant way?
> 
> Antje
> 
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