Concatenate equally sized strings cbind in R
I would like to rearrange matrix b like this:
> b <- matrix(1:24, 6, 4)
> b
[,1] [,2] [,3] [,4]
[1,] 1 7 13 19
[2,] 2 8 14 20
[3,] 3 9 15 21
[4,] 4 10 16 22
[5,] 5 11 17 23
[6,] 6 12 18 24
> cbind(b[1:2, ], b[3:4, ], b[5:6, ])
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
[1,] 1 7 13 19 3 9 15 21 5 11 17 23
[2,] 2 8 14 20 4 10 16 22 6 12 18 24
The number of rows (2 here) will always be the same, but the matrix b will be very large, at about 1M x 100. Is there some quick way I can do this without a for the loop? Thank.
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First split b
the two lines using lapply
, then cbind
subgroup together using do.call
.
do.call(cbind, lapply(seq(1, NROW(b), 2), function(i) b[i:(i+1),]))
# [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
#[1,] 1 7 13 19 3 9 15 21 5 11 17 23
#[2,] 2 8 14 20 4 10 16 22 6 12 18 24
Another way is to split the elements of odd and even strings into two vectors and rbind
their
rbind(do.call(c, data.frame(t(b[(1:NROW(b) %% 2) == 1,]))),
do.call(c, data.frame(t(b[(1:NROW(b) %% 2) == 0,]))))
# X11 X12 X13 X14 X21 X22 X23 X24 X31 X32 X33 X34
#[1,] 1 7 13 19 3 9 15 21 5 11 17 23
#[2,] 2 8 14 20 4 10 16 22 6 12 18 24
Another way, which is for the most part similar to the second approach
do.call(rbind, lapply(split(data.frame(b), 1:2), function(x) do.call(c, data.frame(t(x)))))
# X11 X12 X13 X14 X31 X32 X33 X34 X51 X52 X53 X54
#1 1 7 13 19 3 9 15 21 5 11 17 23
#2 2 8 14 20 4 10 16 22 6 12 18 24
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You can resize the array, move it with aperm
and resize it again:
array(aperm(array(b, c(2,3,4)), c(1,3,2)), c(2,12))
# [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
#[1,] 1 7 13 19 3 9 15 21 5 11 17 23
#[2,] 2 8 14 20 4 10 16 22 6 12 18 24
Another option:
tb <- t(b)
rbind(c(tb[,c(T,F)]), c(tb[,c(F,T)]))
# [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
#[1,] 1 7 13 19 3 9 15 21 5 11 17 23
#[2,] 2 8 14 20 4 10 16 22 6 12 18 24
Step one, change it to 2, 3, 4
:
array(b, c(2,3,4))
, , 1
[,1] [,2] [,3]
[1,] 1 3 5
[2,] 2 4 6
, , 2
[,1] [,2] [,3]
[1,] 7 9 11
[2,] 8 10 12
, , 3
[,1] [,2] [,3]
[1,] 13 15 17
[2,] 14 16 18
, , 4
[,1] [,2] [,3]
[1,] 19 21 23
[2,] 20 22 24
Step two, switch axis / transpose 2 and 3:
aperm(array(b, c(2,3,4)), c(1,3,2))
, , 1
[,1] [,2] [,3] [,4]
[1,] 1 7 13 19
[2,] 2 8 14 20
, , 2
[,1] [,2] [,3] [,4]
[1,] 3 9 15 21
[2,] 4 10 16 22
, , 3
[,1] [,2] [,3] [,4]
[1,] 5 11 17 23
[2,] 6 12 18 24
Step three, resize it to your desired dimensions:
array(aperm(array(b, dim = c(2,3,4)), c(1,3,2)), dim = c(2,12))
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
[1,] 1 7 13 19 3 9 15 21 5 11 17 23
[2,] 2 8 14 20 4 10 16 22 6 12 18 24
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Using split
to cut out the matrix, then run a loop to add dimensions and cbind
:
# number of rows
n <- 2
do.call(cbind, lapply(split(b, (seq(nrow(b))-1) %/% n), matrix, nrow = n))
# [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
# [1,] 1 7 13 19 3 9 15 21 5 11 17 23
# [2,] 2 8 14 20 4 10 16 22 6 12 18 24
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