pm_timeline_ggplot.R

##
## Summary: Plot UK Prime Ministers timeline
##
## GitHub: https://github.com/fredwise/PM_timeline
##
## Author: Fred Tasker
##
## Date Created: 2020-05-30
##
## Copyright (c) Wise Technical Ltd, 2020
## Email: fred@wisetechltd.com
##
library(plotly)
library(jsonlite)
library(ggplot2)
library(lubridate)
library(data.table)
library(magrittr)
prime_ministers <-
  fromJSON(
    'https://raw.githubusercontent.com/TimelineConsortium/Timeline-Data/master/uk-prime-ministers.json'
  ) %>% as.data.table %>% .[,facet:=NULL]

setnames(
  prime_ministers,
  c('content_text', 'category'), #old
  c('name', 'party') #new
)

#Dates
prime_ministers[, start_date := ymd(substr(start_date, 0, 10))]
prime_ministers[, end_date := ymd(substr(end_date, 0, 10))]
setorder(prime_ministers,start_date)

# Colours for the political parties
parties <-
  c("Whig", "Tory", "Conservative", "Peelite", 'Liberal', 'Labour')
party_colours <-
  c("#FF7F00",    "#98285C","#0087DC",'#0660C4','#FDBB30',"#DC241f")

prime_ministers[, party := factor(party, levels = parties, ordered = TRUE)]

#Add a decade column
prime_ministers[, decade := floor_date(start_date, "10 years")]
prime_ministers[, number_in_decade := 1:.N, by = decade]

# Alternate label positions up and down each decade
positions <- c(0.5, -0.5, 1.7, -1.7, 2.9, -2.9)
directions <- c(1,-1)

decades <- unique(prime_ministers$decade)

# A small table to define the direction of vertical lines / text on timeline
line_pos <- data.table(
  "decade" = decades,
  "position" = rep(positions, length.out = (length(decades))),
  "direction" = rep(directions, length.out = (length(decades)))
)

# Merge with prime minister dataset
prime_ministers <- prime_ministers[line_pos, on = 'decade']

# Create a plot position for prime minister name text, so they don't clash
text_offset <- 0.25
prime_ministers[, text_position :=
                  (number_in_decade * text_offset * direction)
                + position]

# Decade data.table to label the axis on timeline
decade_dt <- unique(prime_ministers[,.(decade,direction)])
decade_dt[,decade_label := year(decade)]


## Create plot
p <- ggplot(prime_ministers)

p <- p + labs(col = "Party") + theme_classic()

p <- p + scale_color_manual(values = party_colours,
                            labels = parties,
                            drop = FALSE)
p <- p + scale_fill_manual(values = party_colours,
                           labels = parties,
                           drop = FALSE)

p <- p + geom_hline(yintercept = 0,
                    color = "black",
                    size = 0.3)

# Vertical lines for each decade
p <- p + geom_segment(
  data = prime_ministers[number_in_decade == 1],
  aes(y = position, yend = 0,x=decade, xend = decade),
  color = 'lightgray',
  size = 0.2
)

#Little marker on each decade, jitter so that political parties don't overlap
p <- p + geom_point(aes(x=start_date, y=0,colour = party
), 
shape = 3

)

# Don't show axes, appropriately position legend
p <- p + theme(
  axis.line.y = element_blank(),
  axis.text.y = element_blank(),
  axis.title.x = element_blank(),
  axis.title.y = element_blank(),
  axis.ticks.y = element_blank(),
  axis.text.x = element_blank(),
  axis.ticks.x = element_blank(),
  axis.line.x = element_blank(),
  legend.position = "top",
  legend.text = element_text(size = 10),
  legend.title = element_text(size = 10)
) + guides(col = guide_legend(nrow=1))

# Show decade label
p <- p + geom_text(
  data = decade_dt,
  aes(
    x = decade,
    y = direction*-0.2,
    label = decade_label,
  ),
  size = 3,
  color = 'gray47'
)

# Show project text
p <- p +  geom_label(aes(label = name,fill=party,
                         x=decade
                         ,y = text_position), 
                     size = 3,# family = 'mono',
                     label.padding=unit(0.15,'lines'),colour = 'black',
                     label.size = 0,alpha = 0.3,show.legend = F)


p