How To Add Regression Line On Ggplot

Let us import the neccessary packages first.

In [11]:
library(ggplot2)
library(dplyr)
library(lubridate)

For the example data, we would analyze the covid19 data which is available on the github. We would do a line plot of monthly US data and then plot regression line on top of that plot.

In [2]:
url <- "https://pomber.github.io/covid19/timeseries.json"
covid_data <- fromJSON(url,flatten = TRUE)

covid_data dataframe has data for all the countries, let us look at the data for US only.

In [3]:
us_data <- covid_data$US
In [4]:
typeof(covid_data$US[0,'date'])
'character'

As we see above date is in character format. We need to change this format to date, since we want to group the data by month.

Extract month and year from date column

In [5]:
month = month(as.Date(covid_data$US[,'date'],format="%Y-%m-%d"))
year = year(as.Date(covid_data$US[,'date'],format="%Y-%m-%d"))

Let us merge the month and year column to our dataframe.

In [6]:
us_data <- mutate(us_data,month=month,year=year)

Group data by month and year

We will use the dplyr package to summarize the data.

In [7]:
us_data_gbymonth <- us_data %>% group_by(month,year) %>% summarize(total = sum(confirmed, na.rm = TRUE))
In [8]:
us_data_gbymonth
A grouped_df: 8 × 3
monthyeartotal
<dbl><dbl><int>
12020 38
22020 378
32020 1091068
42020 19552582
52020 45407574
62020 64933835
72020111200861
82020 74821798

Merging separate month and year columns to graph in ggplot2

We will use mdy function from lubridate package to join month and year columns as our x-axis.

In [9]:
ggplot(us_data_gbymonth,aes(mdy(paste(month,1,year)),y=total)) + geom_line()

Add regression line on ggplot

Let add regression line on ggplot now. We would use stat_summary and geom_smoooth function.

In [10]:
options(warn=-1)
ggplot(us_data_gbymonth,aes(x=mdy(paste(month,1,year)),y=total)) + geom_line() + 
       stat_summary(fun.data= mean_cl_normal) +  geom_smooth(method='lm')

`geom_smooth()` using formula 'y ~ x'

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