Basic barplot
To draw the basic barplots we use the in-built data table mtcars.
> head(mtcars) mpg cyl disp hp drat wt qsec vs am gear carb Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4 Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4 Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1 Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1 Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2 Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1
If we wish to plot the frequency of gears found in the database we first need to create a frequency table by aggregating all the unique values of the “gear” column. table() helps aggregate unique values and their frequencies.
> tmp=table(mtcars$gear) 3 4 5 15 12 5 > barplot(tmp)
Grouped barplot
The grouped barplot takes more effort.
> tmp=table(mtcars$cyl, mtcars$gear) 3 4 5 4 1 8 2 6 2 4 1 8 12 0 2 > barplot(tmp,beside = T, legend = paste(rownames(tmp),"cylinders"), col = c(1:length(rownames(tmp))), xlab = "Gears/cylinders", ylab = "Count")
rownames(tmp) extracts unique values of the column “cyl”(cylinders). col cycles through colors. Legend takes the rownames(tmp) as an argument but we want to append the string cylinders so that it is clear what the numbers signify. That is achieved by the paste() command which “pastes” the string “cylinders” at the end.
References:
https://www.statmethods.net/graphs/bar.html
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