Trigonometry with magick, gganimate, and purrr

trigonometry.R

## Purpose: illustrate use of magick, gganimate, and purrr
## Inspiration:
## https://rud.is/b/2016/07/27/u-s-drought-animations-with-the-witchs-brew-purrr-broom-magick/
## and subsequent discussion on magick vs gganimate:
## https://twitter.com/hrbrmstr/status/758304420224466944
library(purrr)
library(ggplot2)
library(gganimate)
library(animation)
library(magick)

# Sequence from 0 to 2pi (= radius of unit circle)
df <- data.frame(x = seq(0, 2 * pi, length.out = 100))

# Create breaks and breaks labels at fractional intervals of pi
breaks <- seq(0, 2, 0.5)
breaks_lbls <- sprintf("%s * pi", as.character(breaks)) %>%
  map(~parse(text = .x)) %>%
  lift(c)(.)

# Animated plot of sin(x) and cos(x) from 0 to 2pi
p_trig <- ggplot(df, aes(x = x, frame = x, cumulative = TRUE)) +
  geom_line(aes(y = sin(x), color = "sin(x)")) +
  geom_line(aes(y = cos(x), color = "cos(x)")) +
  scale_x_continuous(breaks = breaks * pi,
                     labels = breaks_lbls,
                     expand = c(0, 0)) +
  scale_y_continuous(expand = c(0, 0.01)) +
  theme_light() +
  theme(panel.grid.minor = element_blank()) +
  labs(x = "\nx", y = "f(x)\n", color = NULL)

# Generate DF of XY-coordinates of a circle with a given radius and center
circle <- function(t, r = 1, center = c(0, 0)) {
  x <- center[1] + r * cos(t)
  y <- center[2] + r * sin(t)
  data.frame(x, y, id = seq_along(t))
}

df_circle <- circle(df$x)

# Animated plot of unit circle, making a full revolution
p_unit_circle <- ggplot(df_circle, aes(x, y, yend = y, xend = x)) +
  geom_hline(yintercept = 0, color = "grey80", linetype = "dashed") +
  geom_vline(xintercept = 0, color = "grey80", linetype = "dashed") +
  geom_path(color = "grey30") +
  geom_segment(aes(x = 0, y = 0, frame = id), color = "grey80") +
  geom_segment(aes(x = x, y = 0, frame = id,  color = "sin(x)")) +
  geom_segment(aes(x = 0, y = y, frame = id,  color = "cos(x)")) +
  scale_x_continuous(breaks = c(-1, 0, 1), expand = c(0, 0.01)) +
  scale_y_continuous(breaks = c(-1, 0, 1), expand = c(0, 0.01)) +
  coord_equal() +
  theme_light() +
  theme(panel.grid = element_blank(), legend.position = "none") +
  labs(x = "\nx", y = "y\n")

# Save animated plots as GIFs
ani.options(ani.height = 130, interval = 0.001)
gg_animate(p_trig, "trig.gif", title_frame = FALSE, ani.width = 500)
gg_animate(p_unit_circle, "unit_circle.gif", title_frame = FALSE, ani.width = 130)

# Read the two plots and append together
map2(
  "unit_circle.gif" %>% image_read() %>% as.list(),
  "trig.gif" %>% image_read() %>% as.list(),
  ~image_append(c(.x, .y))
  ) %>%
  lift(image_join)(.) %>%
  image_write("result.gif")

# Remove intermediate files
c("trig.gif", "unit_circle.gif") %>% walk(unlink)

# Easier than doing it the old-fashioned way:
# shell(
#   paste(
#     "convert",
#     "\\( unit_circle.gif -coalesce -append \\)",
#     "\\( trig.gif -coalesce -append \\)",
#     "+append -crop x130 -set delay 0.01 +repage result.gif"
#   )
# )