Plot with inwards ticks - ggplot

Plot inwards ticks - ggplot.R

# ==========================================================================
# Example of plot for publication with inwards ticks in ggplot
# ==========================================================================

library(ggplot2)

# ==================================
# create some data
# ==================================
set.seed(1)
DF <- data.frame(year = c(2000:2020),
                 mean = rnorm(n=21, mean=100, sd=10))

# ==================================
# helper function
# ==================================
# Function to return a desired sequence breaks along axes
my.breaks <- function(my.vector, step){
    my.min <- floor(min(my.vector))
    my.max <- ceiling(max(my.vector))
    my.seq <- seq(from = round(my.min/step)*step, 
                  to   = round(my.max/step)*step,
                  by   = step)
    return(my.seq)
}

# ==================================
# Plot
# ==================================
ggplot(data = DF, aes(x = year, y = mean)) +
    # add two vertical lines
    geom_vline(xintercept=c(2010,2013), linetype="dashed", color="gray", lwd=.5) +
    # add lines
    geom_line(lwd=.4) +
    # add points
    # note: use "stroke" to adjust the white border thickness of the point 
    # in order to give the same effect as in base-r plot `type=b`
    geom_point(size=2, shape=21, fill="black", colour="white", stroke=1.2) +
    
    # set axes titles and labels
    scale_x_continuous(name = "Year", breaks = my.breaks(DF$year, step=5)) +
    scale_y_continuous(name = "means", breaks = my.breaks(DF$mean, step=10)) +
    
    # Theme adjustments:
    theme_bw() + # eliminate default background 
    theme(panel.grid.major = element_blank(), # eliminate major grids
          panel.grid.minor = element_blank(), # eliminate minor grids
          # set font family for all text within the plot ("serif" should work as "Times New Roman")
          # note that this can be overridden with other adjustment functions below
          text = element_text(family="serif"),
          # adjust X-axis title
          axis.title.x = element_text(size = 10, face = "bold"),
          # adjust X-axis labels; also adjust their position using margin (acts like a bounding box)
          # using margin was needed because of the inwards placement of ticks
          # http://stackoverflow.com/questions/26367296/how-do-i-make-my-axis-ticks-face-inwards-in-ggplot2
          axis.text.x = element_text(size = 8, margin = unit(c(t = 2.5, r = 0, b = 0, l = 0), "mm")),
          # adjust Y-axis title
          axis.title.y = element_text(size = 10, face = "bold"),
          # adjust Y-axis labels
          axis.text.y = element_text(size = 8, margin = unit(c(t = 0, r = 2.5, b = 0, l = 0), "mm")),
          # length of tick marks - negative sign places ticks inwards
          axis.ticks.length = unit(-1.4, "mm"),
          # width of tick marks in mm
          axis.ticks = element_line(size = .3)
    )

# save as pdf
ggsave("Plot, type b, inwards ticks - ggplot.pdf", width=10, height=7, units="cm")
# save as png
ggsave("Plot, type b, inwards ticks - ggplot.png", width=10, height=7, units="cm", dpi=300)