Select the last n columns of data frame in R

Question

Is there a way to systematically select the last columns of a data frame? I would like to be able to move the last columns to be the first columns, but maintain the order of

Answer 1

Another alternative with dplyr:

mydata2 <- select(mydata, 2:ncol(data),1)  
#select any cols from col2 until the last col and place them before col1

Answer 2

I know this topic is a little dead, but wanted to chime in with a simple dplyr solution:

library(dplyr)

mydata <- mydata %>%
  select(A, B, everything())

Hopefully that helps out any future visitors to this question.

Answer 3

data frames are just lists, so you can rearrange them as you would any list:

newdata <- c(mydata[colNamesToStart],
             mydata[-which(names(mydata) %in% colNamesToStart)])

Answer 4

You can do a similar thing using the SOfun package, available on GitHub.

library(SOfun)

foo <- moveMe(colnames(mydata2), "A, B before num1")

mydata2[, foo]

#  A B num1 num2
#1 A B    1   36
#2 A B    2   37
#3 A B    3   38
#4 A B    4   39
#5 A B    5   40

You can move column names like this example from R Help.

x <- names(mtcars)

x
#[1] "mpg"  "cyl"  "disp" "hp"   "drat" "wt"   "qsec" "vs"   "am"   "gear" "carb"

moveMe(x, "hp first; cyl after drat; vs, am, gear before mpg; wt last")
#[1] "hp"   "vs"   "am"   "gear" "mpg"  "disp" "drat" "cyl"  "qsec" "carb" "wt" 

Answer 5

Using the offset argument in the last_col function, inside select, you can do that.

Below is an example considering the last two columns, and it in a more generic approach.

library(dplyr)

mydata <- mydata %>% select(last_col(offset=c(0,1)), everything())

n <- 2
mydata <- mydata %>% select(last_col(offset=0:(n-1), everything())

Answer 6

You could use something like this:

move_to_start <- function(x, to_move) {
  x[, c(to_move, setdiff(colnames(x), to_move))]
} 

move_to_start(mydata2, c('A', 'B'))

#   A B num1 num2
# 1 A B    1   36
# 2 A B    2   37
# 3 A B    3   38
# 4 A B    4   39
# 5 A B    5   40

Alternatively, if you want to move the last n columns to the start:

move_to_start <- function(x, n) {
  x[, c(tail(seq_len(ncol(x)), n), seq_len(ncol(x) - n))]
} 

move_to_start(mydata2, 2)

#   A B num1 num2
# 1 A B    1   36
# 2 A B    2   37
# 3 A B    3   38
# 4 A B    4   39
# 5 A B    5   40