TidyTuesday - Big Mac Index

For my first #TidyTuesday post, I've attempted a comparison of the 2015 to 2020 movement of the Big Mac index : https://t.co/AOGOvt3ve5#RStats #dataviz #r4ds #ggplot2 pic.twitter.com/1TZTpAo3s0

— Rahul (@rsangole) January 6, 2021

library(tidyverse)
library(ggplot2)
library(ggrepel)
library(ggdark)
library(ggtext)

bigmac <- data.table::fread("big-mac.csv")

bigmac_us_dat <- bigmac %>%
  dplyr::filter(currency_code == "USD") %>%
  dplyr::select(date, bigmac_us_price_USD = local_price)

bigmac_value_dat <- bigmac %>%
  dplyr::select(date,
                currency_code,
                name,
                bigmac_local_price = local_price,
                dollar_ex) %>%
  dplyr::left_join(
    y = bigmac_us_dat,
    on = date
  )

bigmac_value_dat <- bigmac_value_dat %>%
  dplyr::mutate(
    bigmac_ex_rate = bigmac_local_price / bigmac_us_price_USD,
    valuation =  1 - bigmac_ex_rate / dollar_ex
    )

bigmac_value_dat %>%
  dplyr::select(date, name, valuation) %>%
  dplyr::filter(date %in% as.Date(c("2020-07-01", "2015-07-01"))) %>%
  tidyr::pivot_wider(names_from = date, values_from = valuation) %>%
  janitor::clean_names() %>%
  dplyr::mutate(movement = x2020_07_01 - x2015_07_01,
                bw = ifelse(x2020_07_01 > x2015_07_01, "Valuation worse in 5 years", "Valuation better in 5 years"),
                bw = ifelse(name == "United States", "ref", bw),
                bw = factor(bw, levels = c("Valuation worse in 5 years", "Valuation better in 5 years", "ref")),
                name = forcats::fct_reorder(name, x2020_07_01),
                label_pos = ifelse(bw == "Valuation worse in 5 years",
                                   x2020_07_01 + 0.02,
                                   x2020_07_01 - 0.02)) %>%
  dplyr::arrange(movement)  %>%
  tidyr::drop_na()-> to_plot

glimpse(to_plot)

Rows: 42
Columns: 6
$ name        <fct> Sri Lanka, Czech Republic, India, Ukraine, Thailand, Singa…
$ x2015_07_01 <dbl> 0.45409867, 0.40840293, 0.61738434, 0.67662319, 0.33855599…
$ x2020_07_01 <dbl> 0.359218095, 0.334283358, 0.557499169, 0.619139345, 0.2857…
$ movement    <dbl> -0.094880571, -0.074119572, -0.059885175, -0.057483840, -0…
$ bw          <fct> Valuation better in 5 years, Valuation better in 5 years, …
$ label_pos   <dbl> 0.33921810, 0.31428336, 0.53749917, 0.59913935, 0.26574757…

to_plot %>%
  ggplot(aes(y = name, color = bw)) +
  geom_hline(yintercept = 3,
             color = "gray80",
             size = 0.3) +
  geom_vline(xintercept = 0,
             color = "gray90",
             size = 0.2) +
  geom_point(aes(x = x2015_07_01), color = "gray70", size = 1.5) +
  geom_segment(aes(x = x2020_07_01, xend = x2015_07_01, yend = name), color = "gray70") +
  geom_point(
    data = to_plot %>% filter(name != "United States"),
    mapping = aes(x = x2020_07_01),
    size = 2
  ) +
  geom_text(
    data = to_plot %>% filter(bw == "Valuation worse in 5 years"),
    mapping = aes(x = label_pos, y = name, label = name),
    size = 3.5,
    hjust = 0,
    show.legend = FALSE
  ) +
  geom_text(
    data = to_plot %>% filter(bw == "Valuation better in 5 years"),
    mapping = aes(x = label_pos, y = name, label = name),
    size = 3.5,
    hjust = 1,
    show.legend = FALSE
  ) +
  geom_label(
    data = data.frame(
      x = c(-0.5, -0.25, 0, 0.25, 0.50, 0.75),
      y = c(3, 3, 3, 3, 3, 3)
    ),
    mapping = aes(
      x = x,
      y = y,
      label = scales::label_percent()(x)
    ),
    size = 2.8,
    color = "gray30",
    hjust = 0.5,
    label.size = 0,
    label.padding = unit(0.2, "lines")
  ) +
  annotate(
    geom = "curve",
    xend = 0.674,
    yend = 42.5,
    x = 0.674 + 0.04,
    y = 44,
    curvature = .3,
    arrow = arrow(length = unit(2, "mm")),
    color = "#e76f51"
  ) +
  annotate(
    geom = "text",
    x = 0.674 + 0.04 + 0.006,
    y = 44,
    label = "2020",
    hjust = "left",
    size = 3.4,
    color = "#e76f51"
  ) +
  annotate(
    geom = "curve",
    xend = 0.563,
    yend = 42.5,
    x = 0.563 + 0.04,
    y = 44,
    curvature = .3,
    arrow = arrow(length = unit(2, "mm")),
    color = "gray70"
  ) +
  annotate(
    geom = "text",
    x = 0.563 + 0.04 + 0.006,
    y = 44,
    label = "2015",
    hjust = "left",
    size = 3.4,
    color = "gray70"
  ) +
  theme_minimal() +
  theme(
    axis.text = element_blank(),
    panel.grid.major = element_blank(),
    panel.grid.minor = element_blank(),
    axis.title.x = element_text(color = "#264653")
  ) +
  theme(
    legend.position = c(0.14, 0.2),
    legend.title = element_blank(),
    legend.text = element_text(color = "#264653", size = 9.5)
  ) +
  scale_color_manual(values = c("#e76f51", "#2a9d8f")) +
  scale_x_continuous(
    labels = scales::label_percent(),
    breaks = c(-0.5, -0.25, 0, 0.25, 0.5, 0.75),
    expand = c(0, 0.1)
  ) +
  scale_y_discrete(expand = c(-0.1, 7)) +
  annotate(
    geom = "text",
    x = -0.3,
    y = 44,
    label = "Over Valued",
    size = 3.4,
    color = "#264653"
  ) +
  annotate(
    geom = "text",
    x = 0.3,
    y = 44,
    label = "Under Valued",
    size = 3.4,
    color = "#264653"
  ) +
  labs(x = "Big Mac Exchange Rate Valuation", y = "")