# [R] converting each column of a data frame into a matrix with n rows

Davide Piffer pifferdavide at gmail.com
Wed May 17 22:01:08 CEST 2017

```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))
>
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```

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