How to split integer vector in R-CodePudding

I have a vector of integers that I want to split by 3, then I have to order the splitted parts and put bac into integer vector.

as.integer(c(16,9,2,17,10,3,18,11,4,19,12,5,20,13,6,21,14,7,22,15,8))

First step - split like this:

16,9,2
17,10,3
18,11,4
19,12,5
20,13,6
21,14,7
22,15,8

Second step - order:

2,9,16
3,10,17
4,11,18
5,12,19
6,13,20
7,14,21
8,15,22

Third step - put back into integer vector:

2,9,16,3,10,17,4,11,18,5,12,19,6,13,20,7,14,21,8,15,22

CodePudding user response：

With matrix sort:

x <- as.integer(c(16,9,2,17,10,3,18,11,4,19,12,5,20,13,6,21,14,7,22,15,8))
c(apply(matrix(x, ncol = 3, byrow = T), 1, sort))
#[1]  2  9 16  3 10 17  4 11 18  5 12 19  6 13 20  7 14 21  8 15 22

Or with split gl:

unlist(lapply(split(x, gl(length(x) / 3, 3)), sort))

Another shorter approach with split rev (only works if rev and sort are the same):

c(do.call(rbind, rev(split(x, 1:3))))
#[1]  2  9 16  3 10 17  4 11 18  5 12 19  6 13 20  7 14 21  8 15 22

CodePudding user response：

No {dplyr} required here.

x <- as.integer(c(16,9,2,17,10,3,18,11,4,19,12,5,20,13,6,21,14,7,22,15,8))
spl.x <- split(x, ceiling(seq_along(x)/3)) # split the vector
spl.x <- lapply(spl.x, sort) # sort each element of the list
Reduce(c, spl.x) # Reduce list to vector

Second line (splitting) is from this answer: https://stackoverflow.com/a/3321659/2433233

This also works if the length of your original vector is no multiple of 3. The last list element is shorter in this case.

CodePudding user response：

Here is one way to do steps in order:

vector=as.integer(c(16,9,2,17,10,3,18,11,4,19,12,5,20,13,6,21,14,7,22,15,8))
chunk <- 3
n <- length(vector)
r  <- rep(1:ceiling(n/chunk),each=chunk)[1:n]
list_of3 <- split(vector,r)
# > list_of3
# $`1`
# [1] 16  9  2
# 
# $`2`
# [1] 17 10  3
# 
# $`3`
# [1] 18 11  4
# 
# $`4`
# [1] 19 12  5
# 
# $`5`
# [1] 20 13  6
# 
# $`6`
# [1] 21 14  7
# 
# $`7`
# [1] 22 15  8
sorted_list<- lapply(list_of3, function(x)sort(x))
final_vector <- unname(unlist(sorted_list))
final_vector
# > final_vector
# [1]  2  9 16  3 10 17  4 11 18  5 12 19  6 13 20  7 14 21  8 15 22```

CodePudding user response：

Here is one way to do it:

v <- as.integer(c(16,9,2,17,10,3,18,11,4,19,12,5,20,13,6,21,14,7,22,15,8))
res <- split(v, 0:(length(v)-1) %/%3)
unlist(lapply(res, sort), use.names = FALSE)

CodePudding user response：

You can put your data into a 3 column matrix by row, sort rowwise, transpose and convert back to vector:

v <- as.integer(c(16,9,2,17,10,3,18,11,4,19,12,5,20,13,6,21,14,7,22,15,8))
m <- matrix(v, ncol = 3, byrow = TRUE)
c(t(matrix(m[order(row(m), m)], nrow(m), byrow = TRUE)))

[1]  2  9 16  3 10 17  4 11 18  5 12 19  6 13 20  7 14 21  8 15 22

CodePudding user response：

Something like this goes through every step:

v = as.integer(c(16,9,2,17,10,3,18,11,4,19,12,5,20,13,6,21,14,7,22,15,8))

v2 = v  %>% matrix(ncol= 3, byrow = T) 


# [,1] [,2] [,3]
# [1,]   16    9    2
# [2,]   17   10    3
# [3,]   18   11    4
# [4,]   19   12    5
# [5,]   20   13    6
# [6,]   21   14    7
# [7,]   22   15    8

v3 = v2[, rev(seq_len(ncol(v2)))]

# [,1] [,2] [,3]
# [1,]    2    9   16
# [2,]    3   10   17
# [3,]    4   11   18
# [4,]    5   12   19
# [5,]    6   13   20
# [6,]    7   14   21
# [7,]    8   15   22


v4 = v3 %>% as.vector

# [1]  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22