将空白插入载体中，例如R中的小刻度标记

Question

这个问题一般涉及先前SO question涉及在ggplot2轴上创建次刻度标记，特别是对于comment在该问题的答案中建议要插入的函数空白到一个序列可能证明是有用的。

由于我经常在类似的情节中添加次要刻度标记，因此我尝试创建这样的函数（请参阅下面的my answer）。

Answer 1

以下函数允许用户请求向量nth的每个 n ^th 元素x被（1）替换为从向量（empty = TRUE）中省略一个空字符占位符（empty = FALSE;默认值）或（2）。此外，它还提供了请求操作的反向（inverse = TRUE;非默认）的选项。下面举例说明功能。

首先，功能：

every_nth <- function(x, nth, empty = TRUE, inverse = FALSE) 
  {
  if (!inverse) {
    if(empty) {
      x[1:nth == 1] <- ""
      x
      } else {
        x[1:nth != 1]
        }
    } else {
      if(empty) {
        x[1:nth != 1] <- ""
        x
        } else {
          x[1:nth == 1]
        }
    }
}

替换或省略向量元素的一些示例：

numvec <- 0:20
charvec <- LETTERS

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

[1] ""   "1"  "2"  ""   "4"  "5"  ""   "7"  "8"  ""   "10" "11" ""   "13"
[15] "14" ""   "16" "17" ""   "19" "20"

every_nth(charvec, 3)
[1] ""  "B" "C" ""  "E" "F" ""  "H" "I" ""  "K" "L" ""  "N" "O" ""  "Q"
[18] "R" ""  "T" "U" ""  "W" "X" ""  "Z"

## Omit (drop) every 3rd element
every_nth(numvec, 3, empty = FALSE) # vector mode is preserved
[1]  1  2  4  5  7  8 10 11 13 14 16 17 19 20

every_nth(charvec, 3, empty = FALSE)
[1] "B" "C" "E" "F" "H" "I" "K" "L" "N" "O" "Q" "R" "T" "U" "W" "X" "Z"

但是，对于创建次要刻度，最好使用inverse = TRUE选项返回此操作的反转：

## Retain every 3rd element, replacing all others with an empty character
every_nth(numvec, 3, inverse = TRUE) # conversion to character vector
[1] "0"  ""   ""   "3"  ""   ""   "6"  ""   ""   "9"  ""   ""   "12" ""  
[15] ""   "15" ""   ""   "18" ""   ""

every_nth(charvec, 3, inverse = TRUE)
[1] "A" ""  ""  "D" ""  ""  "G" ""  ""  "J" ""  ""  "M" ""  ""  "P" "" 
[18] ""  "S" ""  ""  "V" ""  ""  "Y" ""

## Retain every 3rd element, omitting (dropping) all other elements
every_nth(numvec, 3, empty = FALSE, inverse = TRUE) # vector mode is preserved
[1]  0  3  6  9 12 15 18

every_nth(charvec, 3, empty = FALSE, inverse = TRUE)
[1] "A" "D" "G" "J" "M" "P" "S" "V" "Y"

说明函数在创建次要刻度时的用法：

library(ggplot2)
df <- data.frame(x = rnorm(1000), y = rnorm(1000))

## ggplot2 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))