How to create a graph with two bars and a line in R?

You don't really help us helping you - what you want to achieve requires a lot of things that need to be implemented. Please focus on one problem per question.

Here to make the graph.

Problems:

• make your data long
• Use geom_col and position_dodge
• rescale your proportion data
• For secondary y-axis, consider all the many threads here on SO. (e.g. ggplot with 2 y axes on each side and different scales)

library(tidyverse) mydf <- structure(list(Date = structure(c(18319, 18320, 18321, 18322, 18323, 18324, 18325, 18326, 18327, 18328, 18329, 18330, 18331, 18332, 18333, 18334, 18335, 18336, 18337, 18338, 18339, 18340, 18341, 18342, 18343), class = "Date"), Daily_Cases = c(250, 238, 240, 566, 342, 466, 587, 769, 778, 1247, 1492, 1797, 977, 2313, 2651, 2547, 3497, 3590, 3233, 3526, 4207, 5322, 5986, 6557, 5560 ), Tests = c(2427, 3681, 2966, 2466, 2218, 2511, 3981, 2525, 3997, 5703, 7875, 3889, 6935, 12393, 12857, 11477, 11682, 15729, 13063, 10695, 16884, 17236, 24109, 26336, 25180), Proportion = c(10.3, 6.5, 8.1, 23, 15.4, 18.6, 14.7, 30.5, 19.5, 21.9, 18.9, 46.2, 14.1, 18.7, 20.6, 22.2, 29.9, 22.8, 24.7, 33, 24.9, 30.9, 24.8, 24.9, 22.1)), class = "data.frame", row.names = c(NA, -25L)) mydf_long <- mydf %>% pivot_longer(names_to = 'key', values_to = 'value', Tests:Daily_Cases) ggplot(mydf_long) + geom_col(aes(Date, value, fill = key), position = position_dodge()) + geom_line(aes(Date, Proportion *1000, group = 1)) 

^{Created on 2020-03-23 by the reprex package (v0.3.0)}