every_nth: Add systematic empty elements to a vector
In adamdsmith/nrsmisc: Miscellaneous functions for work

Allows every nth element of a vector x to either be (1) replaced with an empty character placeholder (empty = TRUE; default) or (2) omitted from the vector (empty = FALSE). Additionally, it provides the option of requesting the inverse (inverse = TRUE; not default) of the vector and associated empty or omitted elements. See examples.

1	every_nth(x, nth, empty = TRUE, inverse = FALSE)

`x`	numeric vector
`nth`	numeric scalar indicating which elements of `x` to replace or remove, depending on the choice of the `empty` argument
`empty`	logical; replace `nth` elements with empty character (TRUE; default) or drop from vector (FALSE)?
`inverse`	logical; return the inverse of `x` after elements are set to empty or omitted?

numvec <- 0:20
charvec <- LETTERS

## Replace every 3rd element with an empty character
every_nth(numvec, 3) # conversion to character vector
every_nth(charvec, 3)

## Omit (drop) every 3rd element
every_nth(numvec, 3, empty = FALSE) # vector mode is preserved
every_nth(charvec, 3, empty = FALSE)

## For creation of minor ticks, return the inverse

## Retain every 3rd element, replacing all others with empty character
every_nth(numvec, 3, inverse = TRUE) # conversion to character vector
every_nth(charvec, 3, inverse = TRUE)

## Retain every 3rd element, omitting (dropping) all other elements
every_nth(numvec, 3, empty = FALSE, inverse = TRUE) # vector mode is preserved
every_nth(charvec, 3, empty = FALSE, inverse = TRUE)
## Not run: 
library(ggplot2)
df <- data.frame(x = rnorm(1000), y = rnorm(1000))
## default axis labelling
p <- ggplot(df, aes(x, y)) + geom_point() + theme_bw()
p

## Add minor ticks to axes
custom_breaks <- seq(-3, 3, 0.25)
p +
  scale_x_continuous(breaks = custom_breaks,
  labels = every_nth(custom_breaks, 4, inverse = TRUE)) +
  scale_y_continuous(breaks = custom_breaks,
  labels = every_nth(custom_breaks, 2, inverse = TRUE))

## End(Not run)