10.55 Target as a Factor

20180726 We often build classification models. For such models we want to ensure the target is categoric. Often it is 0/1 and hence is loaded as numeric. We could tell our model algorithm of choice to explicitly do classification or else set the target using base::as.factor() in the formula. Nonetheless it is generally cleaner to do this here and note that this code has no effect if the target is already categoric.

# Ensure the target is categoric.

ds[[target]] %<>% as.factor()

# Confirm the distribution.

ds[target] %>% table()

## rain_tomorrow
##     no    yes 
## 164135  46557

We can visualise the distribution of the target variable using ggplot2 (Wickham, Chang, et al. 2023). The dataset is piped to ggplot2::ggplot() whereby the target is associated through ggplot2::aes_string() (the aesthetics) with the x-axis of the plot. To this we add a graphics layer using ggplot2::geom_bar() to produce the bar chart, with bars having width= 0.2 and a fill= color of "grey". The resulting plot can be seen in Figure @ref(fig:data:plot_target_distribution).

ds %>%
  ggplot(aes_string(x=target)) +
  geom_bar(width=0.2, fill="grey") +
  theme(text=element_text(size=14))

## Warning: `aes_string()` was deprecated in ggplot2 3.0.0.
## ℹ Please use tidy evaluation ideoms with `aes()`

Target variable distribution. Plotting the distribution is useful to gain an insight into the number of observations in each category. As is the case here we often see a skewed distribution.

(#fig:data:plot_target_distribution)Target variable distribution. Plotting the distribution is useful to gain an insight into the number of observations in each category. As is the case here we often see a skewed distribution.

References

Wickham, Hadley, Winston Chang, Lionel Henry, Thomas Lin Pedersen, Kohske Takahashi, Claus Wilke, Kara Woo, Hiroaki Yutani, and Dewey Dunnington. 2023. Ggplot2: Create Elegant Data Visualisations Using the Grammar of Graphics. https://CRAN.R-project.org/package=ggplot2.

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