ggplot - bar plot for two variable from the same data frame

Question

I need to generate a plot with bar graph for two variables.

I can create a column graph for one variable like below

df <- head(mtcars)
df$car <- row.names(df)
ggplot(df) + geom_col(aes(x=car, y=disp))

how to go about getting a chart like below ( created in excel) - essentially I need add bar plot of more than one variable.

Please see https://stackoverflow.com/questions/3099219/plot-with-2-y-axes-one-y-axis-on-the-left-and-another-y-axis-on-the-right — Linus, Dec 21 '17 at 14:17
@Linus - thanks. I will refer to that part for the secondary axis question. — user3206440, Dec 21 '17 at 15:09

score 2 · Accepted Answer · answered Dec 21 '17 at 15:16

2

With ggplot you need to convert data to long format so that one column defines the color and one column defines the y value:

library(tidyr)
df$car = row.names(df)
df_long = gather(df, key = var, value = value, disp, hp)
ggplot(df_long, aes(x = car, y = value, fill = var)) +
  geom_bar(stat = 'identity', position = 'dodge')

answered Dec 21 '17 at 15:16

Gregor Thomas

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how can we bring the legend to the top centered horizontally and set the y-axis label to the variable names !! – user3206440 Dec 21 '17 at 17:13
1

I'm sure if you search the `[ggplot2]` tag for those questions you can find excellent solutions! – Gregor Thomas Dec 21 '17 at 17:25
just an unrelated comment - I see that you are using `=` rather than `<-`. Is this generally accepted practice ? – user3206440 Dec 22 '17 at 09:39
1

It's uncommon, but it's just fine. I prefer it so I do it. – Gregor Thomas Dec 23 '17 at 20:04

ggplot - bar plot for two variable from the same data frame

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