plot_qqline: Plot quantile-quantile (QQ) graphs from data.

Description

This function takes a data table, a quantitative variable (ycol), and a categorical grouping variable (group), if available, and plots a QQ graph using stat_qq and stat_qq_line. Alternatives are plot_histogram, or plot_qqline.

Usage

plot_qqline(
  data,
  ycol,
  group,
  facet,
  symsize = 3,
  s_alpha = 0.8,
  TextXAngle = 0,
  facet_scales = "fixed",
  fontsize = 20,
  symthick,
  linethick,
  ColPal = c("okabe_ito", "all_grafify", "bright", "contrast", "dark", "fishy", "kelly",
    "light", "muted", "pale", "r4", "safe", "vibrant"),
  ColSeq = TRUE,
  ColRev = FALSE,
  ...
)

Value

This function returns a ggplot2 object of class "gg" and "ggplot".

Arguments

data: a data table e.g. data.frame or tibble.
ycol: name of the column (without quotes) with the quantitative variable whose distribution is to be plotted.
group: name of the column containing a categorical grouping variable.
facet: add another variable (without quotes) from the data table to create faceted graphs using facet_wrap.
symsize: size of symbols, default set to 3.
s_alpha: fractional opacity of symbols, default set to 1 (i.e. maximum opacity & zero transparency).
TextXAngle: orientation of text on X-axis; default 0 degrees. Change to 45 or 90 to remove overlapping text.
facet_scales: whether or not to fix scales on X & Y axes for all facet facet graphs. Can be fixed (default), free, free_y or free_x (for Y and X axis one at a time, respectively).
fontsize: parameter of base_size of fonts in theme_classic, default set to size 20.
symthick: thickness of symbol border, default set to fontsize/22.
linethick: thickness of lines, default set to fontsize/22.
ColPal: grafify colour palette to apply (in quotes), default "okabe_ito"; see graf_palettes for available palettes.
ColSeq: logical TRUE or FALSE. Default TRUE for sequential colours from chosen palette. Set to FALSE for distant colours, which will be applied using scale_fill_grafify2.
ColRev: whether to reverse order of colour within the selected palette, default F (FALSE); can be set to T (TRUE).
...: any additional arguments to pass to geom_qq or geom_qq_line.

Details

Note that the function requires the quantitative Y variable first, and a grouping variable as group if required. The graph plots sample quantiles on Y axis & theoretical quantiles on X axis. The X variable is mapped to the fill aesthetic instat_qq and colour aesthetic for the stat_qq_line.

Colours can be changed using ColPal, ColRev or ColSeq arguments. Colours available can be seen quickly with plot_grafify_palette. When only one level is present within group, symbols will receive "ok_orange" colour. ColPal can be one of the following: "okabe_ito", "dark", "light", "bright", "pale", "vibrant, "muted" or "contrast". ColRev (logical TRUE/FALSE) decides whether colours are chosen from first-to-last or last-to-first from within the chosen palette. ColSeq decides whether colours are picked by respecting the order in the palette or the most distant ones using colorRampPalette.

Examples

Run this code

plot_qqline(data = data_cholesterol, 
ycol = Cholesterol, group = Treatment)

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