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

David Winsemius dwinsemius at comcast.net
Wed May 17 22:39:22 CEST 2017

```> On May 17, 2017, at 1:01 PM, Davide Piffer <pifferdavide at gmail.com> wrote:
>
> 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

( y <- data.frame(matrix(1:40, 4, 10)) )
( y.mat <- lapply(y, matrix, nrow=2))

\$X1
[,1] [,2]
[1,]    1    3
[2,]    2    4

\$X2
[,1] [,2]
[1,]    5    7
[2,]    6    8

\$X3
[,1] [,2]
[1,]    9   11
[2,]   10   12

>
> 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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>> and provide commented, minimal, self-contained, reproducible code.
>
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