library(tidyverse)
global.covid19.data.URL = paste(
  "https://github.com/CSSEGISandData/COVID-19",
  "raw/master/csse_covid_19_data/csse_covid_19_time_series",
  "time_series_covid19_confirmed_global.csv", 
  sep='/')

covid19.data <- read_csv(global.covid19.data.URL)

covid19.data <- pivot_longer(covid19.data, cols=`1/22/20`:ncol(covid19.data),
                             names_to = 'date', values_to = 'cases')
covid19.data <- mutate(covid19.data, date=parse_date(date, format="%m/%d/%y"))

us.covid19 <- filter(covid19.data, `Country/Region`=='US')

us.covid19.march <- filter(us.covid19, date >= '2020-03-01' & date <= '2020-03-31')

ggplot(us.covid19.march, aes(x=date, y=cases)) +
  geom_point() +
  geom_line()

fit.cases <- lm(cases ~ date, data = us.covid19.march)
fit.cases

ggplot(us.covid19.march, aes(x=date, y=cases)) +
  geom_point() +
  geom_line() +
  geom_abline(intercept = -92016407, slope = 5020, color = 'blue')

summary(fit.cases)

us.covid19.march <- mutate(us.covid19.march, log2.cases = log(cases,2))

ggplot(us.covid19.march, aes(x=date, y=log2.cases)) +
  geom_point() +
  geom_line()

fit.log2.cases <- lm(log2.cases ~ date, data = us.covid19.march)
fit.log2.cases
summary(fit.log2.cases)
confint(fit.log2.cases)

ggplot(us.covid19.march, aes(x=date, y=log2.cases)) +
  geom_point() +
  geom_line() +
  geom_abline(slope=0.4224, intercept = -7733.8328, color="#00b140")