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SimplyStats thanksgiving Rubik's Cube solution
## transform the input to the output using rubiks-cube transformations and dplyr
require(dplyr)
## provided input
input <- data.frame(matrix(c("h","a","t","t","i","v","i","g","k","s","g","n","n","g","n","i"),
4,
4,
byrow=TRUE,
dimnames=list(NULL,paste0("col",1:4))),
stringsAsFactors=FALSE)
## requested output
output <- data.frame(matrix(c("t","h","a","n","k","s","g","i","v","i","n","g"),
4,
3,
byrow=TRUE,
dimnames=list(NULL,paste0("col",1:3))),
stringsAsFactors=FALSE)
## construct the column rotating function using dplyr commands
## taking care of wrap-around
## allows forwards or backwards rotation through + or - operator
rotate_col <- function(df, colnum) {
if(colnum > 0) {
## rotate the cube 1->4 by 1 step (row3->row4, row2->row3, etc...)
## row4->row1
rotdfcol <- df %>% slice(c(2,3,4,1)) %>% select(colnum)
} else {
## rotate the cube 4->1 by 1 step (row4->row3, row3->row2, etc...)
## row1->row4
colnum <- -colnum
rotdfcol <- df %>% slice(c(4,1,2,3)) %>% select(colnum)
}
newdf <- df
newdf[, colnum] <- rotdfcol
return(newdf)
}
## construct the row rotating function using dplyr commands
## using the same conventions as rotate_col
rotate_row <- function(df, rownum) {
if (rownum > 0) {
rotdfrow <- df %>% select(c(4,1,2,3)) %>% slice(rownum)
} else {
rownum <- -rownum
rotdfrow <- df %>% select(c(2,3,4,1)) %>% slice(rownum)
}
newdf <- df
newdf[rownum, ] <- rotdfrow
return(newdf)
}
## perform rubiks-cube operations to achieve the desired result, utilising row 4 as free spaces
## in no way guaranteed to be the fastest method, just the first one that worked
input %>%
rotate_row(+1) %>%
rotate_col(+4) %>% rotate_col(+4) %>%
rotate_col(-1) %>% rotate_row(+4) %>% rotate_col(-1) %>% rotate_row(-4) %>% rotate_col(+1) %>% rotate_col(+1) %>%
rotate_col(-2) %>% rotate_row(+4) %>% rotate_col(-2) %>% rotate_row(-4) %>% rotate_col(+2) %>% rotate_col(+2) %>%
rotate_col(-3) %>% rotate_row(-4) %>% rotate_col(-3) %>% rotate_row(+4) %>% rotate_col(+3) %>% rotate_col(+3) %>%
rotate_row(+4) %>% rotate_col(-1) %>% rotate_row(-4) %>% rotate_col(+1) %>%
rotate_col(-2) %>% rotate_row(+4) %>% rotate_col(+2) %>%
rotate_row(+4) %>% rotate_col(-3) %>% rotate_row(-4) %>% rotate_col(+3) %>%
rotate_col(-4) %>% rotate_row(+4) %>% rotate_col(+4) %>%
slice(c(1,2,3)) -> solved ## still a 3x4 matrix
## re-shape the solution into a 4x3 matrix
final <- solved %>%
t %>%
c %>%
matrix(4,
3,
byrow=TRUE,
dimnames=list(NULL,paste0("col",1:3))) %>%
data.frame(stringsAsFactors=FALSE)
## check the solution is correct
identical(final, output) # TRUE
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