# Point arrows to specific parts of the data

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tl;dr: Point arrows at your line at defined datum points.

Sometimes to really enhance your picture you need to point at some stuff. Here is a script which will plot vertical lines to show events in your datum plot.

library(ggplot2) # This script will draw points to parts of (interpolated) lines. arrow.length <- 10 touchoff.distance <- 4 # distance between data and start of arrow arrowhead.size <- 2.5 # in millimeters # Simulate some data. set.seed(12) datum.seq <- seq(from = as.Date("2018-01-01"), to = as.Date("2018-12-31"), by = "2 week") xy <- data.frame(datum = rep(datum.seq, times = 2)) xy$count <- c(runif(length(datum.seq), min = 20, max = 50), runif(length(datum.seq), min = 40, max = 60) ) xy$var1 <- rep(c("s1", "s2"), each = length(datum.seq)) # These are the points where we want to point to. topoint <- data.frame(datum = sample(datum.seq, 16) - 7, var1 = rep(c("s1", "s2"), each = 8)) # Function which interpolates per one variable. interpolateOnDate <- function(xy, newdata) { newdata <- newdata[newdata$var1 == unique(xy$var), ] out <- approx(x = xy$datum, y = xy$count, xout = newdata$datum) newdata$count <- out$y newdata } # Apply interpolation to each level of var1 res <- lapply(split(xy, f = xy$var1), FUN = interpolateOnDate, newdata = topoint) res <- do.call(rbind, res) # merge result ggplot(xy, aes(x = datum, y = count)) + theme_bw() + theme(axis.title.y = element_blank()) + geom_point(shape = 1) + geom_path() + geom_segment(data = res, aes(x = datum, y = count + touchoff.distance, xend = datum, yend = count + touchoff.distance + arrow.length), arrow = arrow(length = unit(arrowhead.size, "mm"), ends = "first")) + facet_wrap(~ var1, ncol = 1)

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