Plot two lines from different years in same plot using ggplot2

Question

I'm trying to compare obama's first year approval ratings with Trump's first year approval ratings in a line chart.

The trouble here is that I use two different years obama (2009) and Trump (2017). Can't seem to figure out how to solve this...

rating_comparison %>%
  ggplot(aes(endDate, rating, group = 1)) +
  geom_line(data = filter(rating_comparison, 
                          endDate > "2017-01-28",
                          type == "Overall.A")) +
  geom_line(data = filter(rating_comparison, 
                          president == "Obama" &
                            endDate > "2009-01-25" &
                            endDate < "2010-01-24",
                          type == "Overall.A"))

You'll need to convert the dates into something comparable, like day or week number since taking office. It would help to see the data rating_comparison. — neilfws
– neilfws, Commented Dec 13, 2017 at 22:09
Another strategy would be to add 8 years to all of the Obama dates, so both sets of data would have 2017 for year and plot on the same x values, then set the axis labels to show only month and day, not year + scale_x_date(date_labels = "%b %d") — Jan Boyer
– Jan Boyer, Commented Dec 13, 2017 at 22:57

neilfws · Accepted Answer · 2017-12-14 11:02:42Z

3

I will assume from your code that the data looks something like this:

president   startDate    endDate  rating       type
    Obama  2017-01-17 2017-01-19      59  Overall.A
    Trump  2017-01-25 2017-01-27      42  Overall.A

I also assume that the date columns are of type Date. If not, convert them using something like:

rating_comparison$endDate <- as.Date(rating_comparison$endDate, "%Y-%m-%d")

One approach is to convert each date to "days since the first date", by president. Then plot rating versus day. Of course, this assumes that the "first dates" are somehow comparable - I assume they equate to the first polling date of each presidency.

For example, to colour by president, restricting to the first 365 days:

library(dplyr)
library(ggplot2)
rating_comparison %>% 
  filter(type == "Overall.A") %>%
  group_by(president) %>% 
  mutate(Day = as.numeric(endDate - min(endDate))) %>% 
  ungroup() %>% 
  filter(Day <= 365) %>% 
  ggplot(aes(Day, rating)) + 
    geom_line(aes(color = president))

I grabbed some Gallup data from the web, similar but not identical to yours, to get this result:

edited Dec 14, 2017 at 11:02

answered Dec 13, 2017 at 23:18

neilfws

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2 Comments

Tdebeus Over a year ago

Thanks for you comprehensive answer. obama dates are not from 2017 rather in 2009 of course.

neilfws Over a year ago

Sure. The trick is to make the year irrelevant, by making all dates relative to the first date, for each president.

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