Re: [R] ggplot with major and MINOR tick marks on a log scale

Rui Barradas Tue, 21 Jan 2025 11:38:52 -0800

Às 02:18 de 21/01/2025, Sorkin, John escreveu:

I have used ggplot to create a graph on which the y-axis is on the log scale. 
(see data and code, below.) I would like to add minor tick marks, which will 
also be on the log scale. The data and code are below. I hope somone can tell 
me how I can modify the ggplot code so it produces minor tick marks on a log 
scale.
Thank you,
John

PopByDayByAQIminus <- dget(

   structure(list(Day = c("25", "25", "25", "25", "25", "25", "25",
          "26", "26", "26", "26", "26", "26", "26", "27", "27", "27", "27",
          "27", "27", "27", "28", "28", "28", "28", "28", "28", "28"),
          AQI_Cat = structure(c(1L, 2L, 3L, 4L, 5L, 6L, 7L, 1L, 2L,
                3L, 4L, 5L, 6L, 7L, 1L, 2L, 3L, 4L, 5L, 6L, 7L, 1L, 2L, 3L,
                4L, 5L, 6L, 7L), levels = c("Good", "Moderate", "Unhealthy For 
Some",
                  "Unhealthy", "Very Unhealthy", "Hazardous1", "Hazardous2"),
          class = "factor"), TotalPop = c(3751359, 35043, 4285,
                  11581, 26241, 17456, 18406, 3654557, 153002, 29954, 8452,
                   7719, 10687, 10430, 3654344, 104843, 57277, 24910, 15165,
                   4680, 13582, 3116416, 516504, 149029, 29640, 33468, 10862,
                   18882)),
          class = "data.frame", row.names = c(NA, -28L)))


PopByDayByAQIminus

ggplot(PopByDayByAQIminus,aes(x=AQI_Cat,y=TotalPop/1000000,
                                         
group=Day,color=Day,shape=factor(Day),linetype = factor(Day)))+
   labs(title=title,x="Air Quality Index") +
   geom_point(size=4,alpha=0.7)+
   geom_line(linewidth=1.5,alpha=0.3)+
   theme(axis.text.x=element_text(angle = -15, hjust = 0))+
   scale_y_continuous(trans='log10')
scale_y_continuous(breaks=seq(0,4000000,by=1000000))





John David Sorkin M.D., Ph.D.
Professor of Medicine, University of Maryland School of Medicine;
Associate Director for Biostatistics and Informatics, Baltimore VA Medical 
Center Geriatrics Research, Education, and Clinical Center;
PI Biostatistics and Informatics Core, University of Maryland School of 
Medicine Claude D. Pepper Older Americans Independence Center;
Senior Statistician University of Maryland Center for Vascular Research;

Division of Gerontology and Paliative Care,
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
Cell phone 443-418-5382



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Hello,

Here are two plots with y axis minor breaks tick marks.

They both use guide_axis(minor.ticks = TRUE) but the 2nd plot spaces thetick marks as in logarithmic paper with an auxiliary function taken froma StackOverflow post.

Also, instead of scale_y_continuous(trans = "log10") I have used theequivalent scale_y_log10(), it makes the code simpler and the effect isexactly the same. From ?scale_y_continuous:

"There are three variants that set the transform argument for commonlyused transformations: ⁠scale_*_log10()⁠, ⁠scale_*_sqrt()⁠ and⁠scale_*_reverse()⁠."



Now the code.



PopByDayByAQIminus %>%
  mutate(Day = factor(Day)) %>%
  ggplot(
    aes(x = AQI_Cat, y = TotalPop/1000000,
        group = Day,
        color = Day,
        shape = Day,
        linetype = Day)) +
  labs(x = "Air Quality Index") +
  geom_point(size = 4,alpha = 0.7) +
  geom_line(linewidth = 1.5, alpha = 0.3) +
  theme(axis.text.x = element_text(angle = -15, hjust = 0)) +
  scale_y_log10() +
  guides(y = guide_axis(minor.ticks = TRUE))

#--- And the other plot

# function in this StackOverflow post
# https://stackoverflow.com/a/33179099/8245406
log10_minor_break = function (...){
  function(x) {
    minx         = floor(min(log10(x), na.rm=TRUE)) - 1
    maxx         = ceiling(max(log10(x), na.rm=TRUE)) + 1
    n_major      = maxx - minx + 1
    major_breaks = seq(minx, maxx, by = 1)
    minor_breaks =
      rep(log10(seq(1, 9, by=1)), times = n_major) +
      rep(major_breaks, each = 9)
    return(10^(minor_breaks))
  }
}

PopByDayByAQIminus %>%
  mutate(Day = factor(Day)) %>%
  ggplot(
    aes(x = AQI_Cat, y = TotalPop/1000000,
        group = Day,
        color = Day,
        shape = Day,
        linetype = Day)) +
  labs(x = "Air Quality Index") +
  geom_point(size = 4,alpha = 0.7) +
  geom_line(linewidth = 1.5, alpha = 0.3) +
  theme(axis.text.x = element_text(angle = -15, hjust = 0)) +
  scale_y_log10(
    minor_breaks = log10_minor_break()
  ) +
  guides(y = guide_axis(minor.ticks = TRUE))


Hope this helps,

Rui Barradas

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R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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PLEASE do read the posting guide https://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Re: [R] ggplot with major and MINOR tick marks on a log scale

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