11.5 Bar Chart

20200427

ds %>%
  ggplot(aes(x=wind_dir_3pm)) +
  geom_bar() +
  scale_y_continuous(labels=comma) +  
  labs(x=vnames["wind_dir_3pm"], y="Count")

A common and simple plot is the bar chart which displays bars with a height that corresponds to the number of observations having that value of the variable displayed on the x-axis. We use ggplot2::geom_bar() to add a bar chart layer to a plot. Only an x-axis aesthetic is required using ggplot2::aes() with the x= option. The y-axis is automatically computed.

In our example we pipe the dataset on to ggplot2::ggplot(), specifying the x-axis as the categoric variable wind_dir_3pm (the x-axis). The count is automatically determined from the dataset by ggplot2::geom_bar() which then adds the layer of bars to the plot.

The y-ticks use commas with the ggplot2::scale_continuous() function using the labels=``comma option. It is crucial that for large numbers commas separate the thousands, so that the reader is able to easily read the number. There can be catastrophic outcomes from a misreading of numbers.

The x-axis and y-axis labels are set using ggplot2::labs() with the x= and y= options. The x-label uses the original dataset’s variable name as recorded in the template variable vname (i.e., WindDir3pm). The y-label is set to be Count.

A Bar Chart displays the distribution of the values for a categoric variable, allowing us to compare the frequency of the different categories. The height of each bar represents the frequency of the value of the corresponding category.

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