[R] list of variables to table of factors

[Bill.Venables at csiro.au]

Here is a possibility.  There is only one trick.

> data
  Q1_1 Q1_2 Q1_3 Q1_4 Q1_5 Q1_6 Q1_7 Q1_8
1    5    5    5    4    5    4    5    4
2    4    5    3    5    5    5    3    5
3    4    4    3    4    4    4    4    2
4    5    5    5    5    5    4    4    4
5    5    5    5    5    5    5    5    5
6    3    4    4    3    3    3    4    0
7    4    3    4    4    0    4    5    0
8    2    2    3    1    2    1    1    1
> vals <- sort(unique(as.vector(as.matrix(data))))  ### small trick!
> vals
[1] 0 1 2 3 4 5
> atad <- apply(data, 2, function(x) table(factor(x, levels = vals)))
> atad  ### almost there
  Q1_1 Q1_2 Q1_3 Q1_4 Q1_5 Q1_6 Q1_7 Q1_8
0    0    0    0    0    1    0    0    2
1    0    0    0    1    0    1    1    1
2    1    1    0    0    1    0    0    1
3    1    1    3    1    1    1    1    0
4    3    2    2    3    1    4    3    2
5    3    4    3    3    4    2    3    2
> atad <- t(atad)  ### not sure why you want this!
> atad
     0 1 2 3 4 5
Q1_1 0 0 1 1 3 3
Q1_2 0 0 1 1 2 4
Q1_3 0 0 0 3 2 3
Q1_4 0 1 0 1 3 3
Q1_5 1 0 1 1 1 4
Q1_6 0 1 0 1 4 2
Q1_7 0 1 0 1 3 3
Q1_8 2 1 1 0 2 2
>  

You need to be careful, though.  You started with a data frame, and this is a matrix:

> class(atad)
[1] "matrix"

You can turn it into a data frame, but...

> data.frame(atad)
     X0 X1 X2 X3 X4 X5
Q1_1  0  0  1  1  3  3
Q1_2  0  0  1  1  2  4
Q1_3  0  0  0  3  2  3
Q1_4  0  1  0  1  3  3
Q1_5  1  0  1  1  1  4
Q1_6  0  1  0  1  4  2
Q1_7  0  1  0  1  3  3
Q1_8  2  1  1  0  2  2
> 

the column names will be transformed to syntactially valid names.  Just be aware of this.

Bill Venables.



Bill Venables
http://www.cmis.csiro.au/bill.venables/ 


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of arademaker
Sent: Sunday, 29 March 2009 8:40 AM
To: r-help at r-project.org
Subject: [R] list of variables to table of factors

Sorry about the simple question. Is there any function to transform a
data.frame like this (rows are observations and columns are
variables):

  Q1_1 Q1_2 Q1_3 Q1_4 Q1_5 Q1_6 Q1_7 Q1_8
1    5    5    5    4    5    4    5    4
2    4    5    3    5    5    5    3    5
3    4    4    3    4    4    4    4    2
4    5    5    5    5    5    4    4    4
5    5    5    5    5    5    5    5    5
6    3    4    4    3    3    3    4    0
7    4    3    4    4    0    4    5    0
8    2    2    3    1    2    1    1    1

Into a data.frame where the rows are the columns of the previous one
and each column is a possible value for that variable. The data are
the counting of observations for each variable vs possible value:

          1   2  3  4  5
Q1_1  0   1  1  3  3
Q1_2  0   1  1  2  4
...

I know that I can use:

tapply(x[["Q1_1"]],factor(x[["Q1_1"]], levels=1:5), length)

to compute each row and than create a matrix of it. But I wonder if
there is some function already defined for doing this transformation.

Cheers,
Alexandre

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