Histograms with lessR

## The Histogram

For a general presentation of using `R` and `lessR`, including examples of bar charts, select one or both of the following sources.

- online book chapter
- within a working `R` session, enter `browseVignettes("lessR")`, then select the `Histogram` vignette
- within a working `R` session, enter `?Histogram` to access the manual that describes the `Histogram()` function

### Bins

How to display the frequencies of the data values for a continuous variable such as Age, Salary, MPG, Gallons, or Height? In contrast to the relatively few unique values of a categorical value, a continuous variable has many potential unique values. How many potential values? Generally there are too many unique data values to plot each individually on a single visualization. The solution is to form bins, a sequence of adjacent, non-overlapping intervals, each generally of the same size. Each bin contains approximately equal data values.

### Construct the Histogram

Place each data value for a continuous variable into its corresponding bin. Construct the histogram as a set of adjacent bars, one bar per bin. The height of each bar is proportional to the frequency of its values. Adjacent bars of a histogram share a common side, no gaps between bars to indicate the underlying continuity.

### Artifacts

The final choice of bin width is subjective, so different bin widths should generally be explored beyond whatever default bin width is provided by the computer. The most efficient way to set bin width manually is to first obtain a histogram with the default bin width, then manually modify the bin width. Select a bin width to display as much detail as possible for the sample size without excessive random noise.

The bin width artifact occurs when the change in the bin width of a histogram changes the shape of the histogram. The bin shift artifact occurs when the starting point of a histogram changes, and the shape of the histogram also changes.

### Palettes Addressed to Color-Blindness

Typical color palettes are not designed to account for color-blindness. Two palettes included in `lessR` do permit more sensitivity to differentiate among objects with various types of color blindness: `Okabe-Ito` and `viridis`. These are qualitative palettes, which means that the hue varies across the plotted objects, here bars. Specify these, or other palettes, as the value for the `fill` parameter, available both by entering a function call in the R console or via the interactive analysis.

### Parameters

For the full list of `Histogram()` parameters, see the manual obtained by entering `?Histogram`. These listed parameters are those provided in the interactive session from `interact("Histogram")`.

#### `x`-variable

  The numerical variable from which to compute the bins and construct the histogram.

#### Bins

bin_width
  width of the bins
bin_start
  starting value of the first bin

#### Colors

fill
  interior color of a bar
color
  exterior color of a bar, i.e., its border
transparency
  transparency level of `0` (none) to `1` (completely transparent)

#### Values, Cumulate

values
  type of value displayed, `"%"` for percent, `"input"` for entered data values, `"off"` for none
cumulate
  specifies to display the cumulative histogram or both cumulative and regular histograms with values of `"off"`, `"on"`, and `"both"`.

#### Smooth

density
  smoothed density curve, initially at a default bandwidth
show_histogram
  if `TRUE`, show the histogram behind the density curve
rug
  if `TRUE`, show a direct display of density as a narrow band beneath the density curve
type
  general density, normal density, or both
bandwidth
  determines the smoothness of the resulting density curve, larger values yield more smooth curves
fill_general
  interior color of the general density curve
fill_normal
  interior color of the normal density curve

#### Save

width
  width of saved pdf file, in inches
height
  height of saved pdf file, in inches