library(ggplot2)

Unit <- c("A", "B", "C", "D") #character objects need quotes
Yes <- c(50, 65, 20, 41)
No <- c(70, 67, 40, 20)
Missing <- c(10, 12, 8, 7)
df <- data.frame(Unit, Yes, No, Missing)

require(tidyr)
df.long <- gather(df, Unit)
colnames(df.long) <- c("Unit", "variable", "value")

ggplot(data = df.long, aes(x = Unit, y = value, fill = variable)) +
       geom_col(position = position_dodge())