R help - May 2017 - converting each column of a data frame into a matrix with n rows

I need to convert each vector of a dataframe into a matrix with 2 rows
and 2 columns (i.e. contingency table).
Note I don't want to convert the entire df into a matrix! I want to
apply a function that converts each 4 elements vector of a df into a 2
x 2 matrix.

I wrote something like this, but it will not work:

f_matrix=function(x){ matrix (x)
  nrow=2}
matrix_y=apply(y,2,function(x) f_matrix (x))

> On May 17, 2017, at 12:18 PM, Davide Piffer <pifferdavide at
gmail.com> wrote:
> 
> I need to convert each vector of a dataframe into a matrix with 2 rows
> and 2 columns (i.e. contingency table).
> Note I don't want to convert the entire df into a matrix! I want to
> apply a function that converts each 4 elements vector of a df into a 2
> x 2 matrix.
> 
> I wrote something like this, but it will not work:
> 
> f_matrix=function(x){ matrix (x)
>  nrow=2}
> matrix_y=apply(y,2,function(x) f_matrix (x))
Maybe it shold be:

matrix_y_list = lapply(y, function(x) f_matrix (x) )

> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius
Alameda, CA, USA

Not really enough info here since you don't specify much about the data
frame or how the results should be provided, but maybe something like this:

y <- data.frame(matrix(1:100, 10, 10))
y.mat <- lapply(y, matrix, nrow=2)
str(y.mat)
List of 10
 $ X1 : int [1:2, 1:5] 1 2 3 4 5 6 7 8 9 10
 $ X2 : int [1:2, 1:5] 11 12 13 14 15 16 17 18 19 20
 $ X3 : int [1:2, 1:5] 21 22 23 24 25 26 27 28 29 30
 $ X4 : int [1:2, 1:5] 31 32 33 34 35 36 37 38 39 40
 $ X5 : int [1:2, 1:5] 41 42 43 44 45 46 47 48 49 50
 $ X6 : int [1:2, 1:5] 51 52 53 54 55 56 57 58 59 60
 $ X7 : int [1:2, 1:5] 61 62 63 64 65 66 67 68 69 70
 $ X8 : int [1:2, 1:5] 71 72 73 74 75 76 77 78 79 80
 $ X9 : int [1:2, 1:5] 81 82 83 84 85 86 87 88 89 90
 $ X10: int [1:2, 1:5] 91 92 93 94 95 96 97 98 99 100


-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352


-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Davide Piffer
Sent: Wednesday, May 17, 2017 2:18 PM
To: r-help at r-project.org
Subject: [R] converting each column of a data frame into a matrix with n rows

I need to convert each vector of a dataframe into a matrix with 2 rows
and 2 columns (i.e. contingency table).
Note I don't want to convert the entire df into a matrix! I want to
apply a function that converts each 4 elements vector of a df into a 2
x 2 matrix.

I wrote something like this, but it will not work:

f_matrix=function(x){ matrix (x)
  nrow=2}
matrix_y=apply(y,2,function(x) f_matrix (x))

______________________________________________
R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Thanks! This gets closer to the solution but a small problem remains.
I get 2 rows and only one column, whereas I need a 2x2 matrix (like a
contingency table for Fisher's exact test).Also another issue is it
repeats the first number of the column, instead of using all 4.
For example, first vector of df is=c(564,3825,125, 377

I get:

         [,1]
[1,] 564.3112
[2,] 564.3112


But I should get

       [,1]   [.2]
[1,]564   125
[2,] 3825  377

On 17 May 2017 at 22:35, David L Carlson <dcarlson at tamu.edu>
wrote:
> Not really enough info here since you don't specify much about the data
frame or how the results should be provided, but maybe something like this:
>
> y <- data.frame(matrix(1:100, 10, 10))
> y.mat <- lapply(y, matrix, nrow=2)
> str(y.mat)
> List of 10
>  $ X1 : int [1:2, 1:5] 1 2 3 4 5 6 7 8 9 10
>  $ X2 : int [1:2, 1:5] 11 12 13 14 15 16 17 18 19 20
>  $ X3 : int [1:2, 1:5] 21 22 23 24 25 26 27 28 29 30
>  $ X4 : int [1:2, 1:5] 31 32 33 34 35 36 37 38 39 40
>  $ X5 : int [1:2, 1:5] 41 42 43 44 45 46 47 48 49 50
>  $ X6 : int [1:2, 1:5] 51 52 53 54 55 56 57 58 59 60
>  $ X7 : int [1:2, 1:5] 61 62 63 64 65 66 67 68 69 70
>  $ X8 : int [1:2, 1:5] 71 72 73 74 75 76 77 78 79 80
>  $ X9 : int [1:2, 1:5] 81 82 83 84 85 86 87 88 89 90
>  $ X10: int [1:2, 1:5] 91 92 93 94 95 96 97 98 99 100
>
>
> -------------------------------------
> David L Carlson
> Department of Anthropology
> Texas A&M University
> College Station, TX 77840-4352
>
>
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Davide
Piffer
> Sent: Wednesday, May 17, 2017 2:18 PM
> To: r-help at r-project.org
> Subject: [R] converting each column of a data frame into a matrix with n
rows
>
> I need to convert each vector of a dataframe into a matrix with 2 rows
> and 2 columns (i.e. contingency table).
> Note I don't want to convert the entire df into a matrix! I want to
> apply a function that converts each 4 elements vector of a df into a 2
> x 2 matrix.
>
> I wrote something like this, but it will not work:
>
> f_matrix=function(x){ matrix (x)
>   nrow=2}
> matrix_y=apply(y,2,function(x) f_matrix (x))
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.