A dplyr-like verb to move columns in a data frame

move.R

vars_select_pos <- function(.vars, ...) {
  match(tidyselect::vars_select(.vars, ...), .vars)
}

before <- function(..., .vars = tidyselect::peek_vars()) {
  min(vars_select_pos(.vars, ...)) - 1
}

after <- function(..., .vars = tidyselect::peek_vars()) {
  max(vars_select_pos(.vars, ...))
}

move <- function(.data, .position, ...) {
  pos <- tidyselect::with_vars(names(.data), .position)
  if ((n <- length(pos)) != 1) {
    stop("`.position` must have length 1, not ", n, ".", call. = FALSE)
  }

  sels <- setdiff(vars_select_pos(names(.data), ...), pos)
  head <- setdiff(seq_len(pos), sels)

  select(.data, !!!head, !!!sels, everything())
}

library(dplyr)

head(iris) %>%
  move(before(1), Species)
#>   Species Sepal.Length Sepal.Width Petal.Length Petal.Width
#> 1  setosa          5.1         3.5          1.4         0.2
#> 2  setosa          4.9         3.0          1.4         0.2
#> 3  setosa          4.7         3.2          1.3         0.2
#> 4  setosa          4.6         3.1          1.5         0.2
#> 5  setosa          5.0         3.6          1.4         0.2
#> 6  setosa          5.4         3.9          1.7         0.4

head(iris) %>%
  move(after(last_col()), 1)
#>   Sepal.Width Petal.Length Petal.Width Species Sepal.Length
#> 1         3.5          1.4         0.2  setosa          5.1
#> 2         3.0          1.4         0.2  setosa          4.9
#> 3         3.2          1.3         0.2  setosa          4.7
#> 4         3.1          1.5         0.2  setosa          4.6
#> 5         3.6          1.4         0.2  setosa          5.0
#> 6         3.9          1.7         0.4  setosa          5.4

head(iris) %>%
  move(after(ends_with("Length")), ends_with("Width"))
#>   Sepal.Length Petal.Length Sepal.Width Petal.Width Species
#> 1          5.1          1.4         3.5         0.2  setosa
#> 2          4.9          1.4         3.0         0.2  setosa
#> 3          4.7          1.3         3.2         0.2  setosa
#> 4          4.6          1.5         3.1         0.2  setosa
#> 5          5.0          1.4         3.6         0.2  setosa
#> 6          5.4          1.7         3.9         0.4  setosa

head(iris) %>%
  move(ends_with("Length"), ends_with("Width"))
#> Error: `.position` must have length 1, not 2.

# alternative API, matching tibble::add_column()
position_from_before_after <- function(.before, .after, .vars) {
  before_is_null <- rlang::quo_is_null(enquo(.before))
  after_is_null <- rlang::quo_is_null(enquo(.after))

  if (!xor(before_is_null, after_is_null)) {
    stop("Must supply either `.before` or `.after`.", call. = FALSE)
  }

  if (before_is_null) {
    after({{ .after }}, .vars = .vars)
  } else {
    before({{ .before }}, .vars = .vars)
  }
}

move <- function(.data, ..., .before = NULL, .after = NULL) {
  pos <- position_from_before_after({{ .before }}, {{ .after }}, names(.data))

  sels <- setdiff(vars_select_pos(names(.data), ...), pos)
  head <- setdiff(seq_len(pos), sels)

  select(.data, !!!head, !!!sels, everything())
}

head(iris) %>%
  move(Species, .before = 1)
#>   Species Sepal.Length Sepal.Width Petal.Length Petal.Width
#> 1  setosa          5.1         3.5          1.4         0.2
#> 2  setosa          4.9         3.0          1.4         0.2
#> 3  setosa          4.7         3.2          1.3         0.2
#> 4  setosa          4.6         3.1          1.5         0.2
#> 5  setosa          5.0         3.6          1.4         0.2
#> 6  setosa          5.4         3.9          1.7         0.4

head(iris) %>%
  move(1, .after = last_col())
#>   Sepal.Width Petal.Length Petal.Width Species Sepal.Length
#> 1         3.5          1.4         0.2  setosa          5.1
#> 2         3.0          1.4         0.2  setosa          4.9
#> 3         3.2          1.3         0.2  setosa          4.7
#> 4         3.1          1.5         0.2  setosa          4.6
#> 5         3.6          1.4         0.2  setosa          5.0
#> 6         3.9          1.7         0.4  setosa          5.4

head(iris) %>%
  move(ends_with("Width"), .after = ends_with("Length"))
#>   Sepal.Length Petal.Length Sepal.Width Petal.Width Species
#> 1          5.1          1.4         3.5         0.2  setosa
#> 2          4.9          1.4         3.0         0.2  setosa
#> 3          4.7          1.3         3.2         0.2  setosa
#> 4          4.6          1.5         3.1         0.2  setosa
#> 5          5.0          1.4         3.6         0.2  setosa
#> 6          5.4          1.7         3.9         0.4  setosa

head(iris) %>%
  move(.after = Species, ends_with("Length"), ends_with("Width"))
#>   Species Sepal.Length Petal.Length Sepal.Width Petal.Width
#> 1  setosa          5.1          1.4         3.5         0.2
#> 2  setosa          4.9          1.4         3.0         0.2
#> 3  setosa          4.7          1.3         3.2         0.2
#> 4  setosa          4.6          1.5         3.1         0.2
#> 5  setosa          5.0          1.4         3.6         0.2
#> 6  setosa          5.4          1.7         3.9         0.4