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Plot the distribution of a variable with conditioning

Source: R/distPlot.R
distPlot.Rd

This function plots the distribution of one or more pollutants or other variables as a histogram, kernel density estimate function, or empirical cumulative distribution function. The choice of method comes with trade-offs; for example, histograms are often more easily interpretable but can easily get cluttered and are heavily dependent on bin width, whereas density functions appear 'cleaner' with many overlapping groups, but can be more challenging to interpret.

Usage

distPlot(
  mydata,
  pollutant = "nox",
  method = c("histogram", "freqpoly", "density", "ecdf"),
  binwidth = NULL,
  bins = 30,
  position = NULL,
  log = FALSE,
  group = "default",
  type = "default",
  cols = "hue",
  theme = "default",
  key.title = group,
  key.position = "top",
  ref.x = NULL,
  ref.y = NULL,
  auto.text = TRUE,
  plot = TRUE,
  ...
)

Arguments

mydata

A data frame.

pollutant

Name of the pollutant(s) to plot contained in mydata.

method

One of: "histogram", "freqpoly", "density", or "ecdf". Note that "freqpoly" is effectively a line chart equivalent of a histogram, and may appear less cluttered with many groups.

binwidth, bins

Used when method = "histogram" or "freqpoly". binwidth sets the width of the bins. bins sets the number of bins, defaulting to 30. bins is overridden by binwidth.

position

A string representing a ggplot2 "position" - see ggplot2::position_identity() and similar functions. When NULL, will use "stack" for histograms and "identity" for other methods. Also useful is "fill" in conjunction with the group argument which will 'normalise' the y-axis to show a percentage rather than an absolute count or density estimate. Not used when method = "ecdf", which must be "identity". Note that density functions will use 'count' over 'density' for non-identity positions.

log

Should the x-axis appear on a log scale? The default is FALSE. If TRUE a well-formatted log10 scale is used.

group

This sets the grouping variable to be used. For example, if a data frame had a column site setting group = "site" will plot all sites together in each panel. Passed to cutData().

type

Character string(s) defining how data should be split/conditioned before plotting. "default" produces a single panel using the entire dataset. Any other options will split the plot into different panels - a roughly square grid of panels if one type is given, or a 2D matrix of panels if two types are given. type is always passed to cutData(), and can therefore be any of:

  • A built-in type defined in cutData() (e.g., "season", "year", "weekday", etc.). For example, type = "season" will split the plot into four panels, one for each season.

  • The name of a numeric column in mydata, which will be split into n.levels quantiles (defaulting to 4).

  • The name of a character or factor column in mydata, which will be used as-is. Commonly this could be a variable like "site" to ensure data from different monitoring sites are handled and presented separately. It could equally be any arbitrary column created by the user (e.g., whether a nearby possible pollutant source is active or not).

Most openair plotting functions can take two type arguments. If two are given, the first is used for the columns and the second for the rows.

cols

Colours to use for plotting. Can be a pre-set palette (e.g., "turbo", "viridis", "tol", "Dark2", etc.) or a user-defined vector of R colours (e.g., c("yellow", "green", "blue", "black") - see colours() for a full list) or hex-codes (e.g., c("#30123B", "#9CF649", "#7A0403")). Alternatively, can be a list of arguments to control the colour palette more closely (e.g., palette, direction, alpha, etc.). See openColours() and colourOpts() for more details.

theme

A string representing an overall plot theme, defaulting to "default". This option makes sweeping changes to non-data plot features such as fonts, colours, line widths, and so on, and may also change default arguments like cols if not set by the user. Can also take a ggplot2::theme() object, which will be used to modify the "default" theme. Pre-set options include:

  • "default", a lattice-inspired theme resembling the traditional openair look, with structured panels and visible gridlines.

  • "dark", a dark-background variant of the default theme, designed for presentations and low-light viewing, using high-contrast text and colour palettes optimised for visibility against dark panels.

  • "modern", a minimalist, contemporary theme inspired by tools such as Plotly and Observable Plot, with reduced visual clutter, horizontal emphasis in gridlines, a clean legend style, and typography suited to dashboards and reports.

  • "soft", a low-contrast, 'editorial' theme with warm background tones, subtle gridlines, and gently desaturated colours, designed for reports and publication-style figures, particularly where a calmer appearance improves readability.

  • "print", a strictly greyscale theme optimised for black-and-white reproduction, with stronger structural elements such as clearer gridlines and axis definitions to ensure good contrast and readability in printed or photocopied outputs.

Please note that if a global theme is set with ggplot2::theme_set() to anything other than the default ggplot2::theme_grey(), the selected openair theme will not be fully applied; instead, only minimal adjustments (such as legend positioning) will be made.

key.title

Used to set the title of the legend. The legend title is passed to quickText() if auto.text = TRUE.

key.position

Location where the legend is to be placed. Allowed arguments include "top", "right", "bottom", "left" and "none", the last of which removes the legend entirely.

ref.x

Either a single value or values representing the x axis intercepts to draw lines, or a list such as that provided by refOpts() to customise the colour/width/type/etc. of each line. See refOpts() for more details.

ref.y

Either a single value or values representing the y axis intercepts to draw lines, or a list such as that provided by refOpts() to customise the colour/width/type/etc. of each line. See refOpts() for more details.

auto.text

Either TRUE (default) or FALSE. If TRUE titles and axis labels will automatically try and format pollutant names and units properly, e.g., by subscripting the "2" in "NO2". Passed to quickText().

plot

When openair plots are created they are automatically printed to the active graphics device. plot = FALSE deactivates this behaviour. This may be useful when the plot data is of more interest, or the plot is required to appear later (e.g., later in a Quarto document, or to be saved to a file).

...

Addition options are passed on to cutData() for type handling. Some additional arguments are also available, varying somewhat in different plotting functions:

  • title, subtitle, caption, tag, xlab and ylab control the plot title, subtitle, caption, tag, x-axis label and y-axis label, passed to ggplot2::labs() via quickText() if auto.text = TRUE.

  • xlim, ylim and limits control the limits of the x-axis, y-axis and colorbar scales.

  • ncol and nrow set the number of columns and rows in a faceted plot.

  • scales can be "fixed", "free_x", "free_y" or "free" to control whether axes are shared across facets when using type. Also supported are the legacy x.relation and y.relation, which can be either "same" or "free" and get remapped to scales automatically.

  • Similarly, space, axes, axis.labels, switch and strip.position can be used to customise the appearance of faceted plots. See ggplot2::facet_wrap() and ggplot2::facet_grid() for the arguments these take.

  • fontsize overrides the overall font size of the plot by setting the text argument of ggplot2::theme(). It may also be applied proportionately to any openair annotations (e.g., N/E/S/W labels on polar coordinate plots).

  • Various graphical parameters are also supported: linewidth, linetype, shape, size, border, and alpha. Not all parameters apply to all plots. These can take a single value, or a vector of multiple values - e.g., shape = c(1, 2) - which will be recycled to the length of values needed.

  • lineend, linejoin and linemitre tweak the appearance of line plots; see ggplot2::geom_line() for more information.

  • In polar coordinate plots, annotate = FALSE will remove the N/E/S/W labels and any other annotations.

Value

an openair object

Author

Jack Davison

Examples

distPlot(mydata, pollutant = "no2", group = "season")


if (FALSE) { # \dontrun{
distPlot(
  mydata,
  pollutant = "no2",
  group = "weekend",
  method = "density",
  cols = "tol"
)

distPlot(
  mydata,
  pollutant = "no2",
  group = "wd",
  position = "fill",
  wd.res = 4,
  alpha = 0.75,
  cols = "tol"
)
} # }