Extract a series of consecutive vectors from a matrix
I have a large matrix, let's say for simplicity:
> mat = matrix(c(1:50), ncol = 5)
> mat
[,1] [,2] [,3] [,4] [,5]
[1,] 1 11 21 31 41
[2,] 2 12 22 32 42
[3,] 3 13 23 33 43
[4,] 4 14 24 34 44
[5,] 5 15 25 35 45
[6,] 6 16 26 36 46
[7,] 7 17 27 37 47
[8,] 8 18 28 38 48
[9,] 9 19 29 39 49
[10,] 10 20 30 40 50
I want to sequentially extract all possible vertical vectors of 3 elements from each column for example. (1,2,3), (2,3,4), ..., (11,12,13), (12,13,14), ... and generate a 3-x-X matrix consisting of all these vectors. Something that looks like this:
[,1] [,2] [,3]
[1,] 1 2 3
[2,] 2 3 4
[3,] 3 4 5
etc. . . .
[5,] 11 12 13
[6,] 12 13 14
[7,] 13 14 15
etc. .. .. ..
[9,] 21 22 23
[10,] 22 23 24
I tried to use the lapply and cbind functions as well as the more general for loop, but it shows "wrong number of dimensions". Thank you for your help!
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2 answers
We can do this with base R
do.call(rbind, lapply(as.data.frame(mat), embed, 3))[,3:1]
# [,1] [,2] [,3]
# [1,] 1 2 3
# [2,] 2 3 4
# [3,] 3 4 5
# [4,] 4 5 6
# [5,] 5 6 7
# [6,] 6 7 8
# [7,] 7 8 9
# [8,] 8 9 10
# [9,] 11 12 13
#[10,] 12 13 14
#[11,] 13 14 15
#[12,] 14 15 16
#[13,] 15 16 17
#[14,] 16 17 18
#[15,] 17 18 19
#[16,] 18 19 20
#[17,] 21 22 23
#[18,] 22 23 24
#[19,] 23 24 25
#[20,] 24 25 26
#[21,] 25 26 27
#[22,] 26 27 28
#[23,] 27 28 29
#[24,] 28 29 30
#[25,] 31 32 33
#[26,] 32 33 34
#[27,] 33 34 35
#[28,] 34 35 36
#[29,] 35 36 37
#[30,] 36 37 38
#[31,] 37 38 39
#[32,] 38 39 40
#[33,] 41 42 43
#[34,] 42 43 44
#[35,] 43 44 45
#[36,] 44 45 46
#[37,] 45 46 47
#[38,] 46 47 48
#[39,] 47 48 49
#[40,] 48 49 50
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Like this?
EDIT: Changed function from 'print' to 'c' in rollapply based on Grothendieck's suggestion in the comment.
library(zoo)
do.call(rbind,lapply(as.data.frame(mat), function(x) rollapply(x,width=3,c)))
[,1] [,2] [,3]
[1,] 1 2 3
[2,] 2 3 4
[3,] 3 4 5
[4,] 4 5 6
[5,] 5 6 7
[6,] 6 7 8
[7,] 7 8 9
[8,] 8 9 10
[9,] 11 12 13
[10,] 12 13 14
[11,] 13 14 15
[12,] 14 15 16
[13,] 15 16 17
[14,] 16 17 18
[15,] 17 18 19
[16,] 18 19 20
[17,] 21 22 23
[18,] 22 23 24
[19,] 23 24 25
[20,] 24 25 26
[21,] 25 26 27
[22,] 26 27 28
[23,] 27 28 29
[24,] 28 29 30
[25,] 31 32 33
[26,] 32 33 34
[27,] 33 34 35
[28,] 34 35 36
[29,] 35 36 37
[30,] 36 37 38
[31,] 37 38 39
[32,] 38 39 40
[33,] 41 42 43
[34,] 42 43 44
[35,] 43 44 45
[36,] 44 45 46
[37,] 45 46 47
[38,] 46 47 48
[39,] 47 48 49
[40,] 48 49 50
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