Grouped bar plots with error bars

Creates a bar plot showing group means with error bars showing confidence intervals, broken down by one or two grouping factors.

Usage

bars(
  formula,
  data = NULL,
  heightFun = mean,
  errorFun = ciMean,
  yLabel = NULL,
  xLabels = NULL,
  main = "",
  ylim = NULL,
  barFillColour = NULL,
  barLineWidth = 2,
  barLineColour = "black",
  barSpaceSmall = 0.2,
  barSpaceBig = 1,
  legendLabels = NULL,
  legendDownShift = 0,
  legendLeftShift = 0,
  errorBarLineWidth = 1,
  errorBarLineColour = "grey40",
  errorBarWhiskerWidth = 0.2
)

Arguments

formula: A two-sided formula of the form response ~ group1 or response ~ group1 + group2. The response variable must be numeric; grouping variables must be factors.
data: An optional data frame containing the variables named in formula. If omitted, the variables are looked up in the workspace.
heightFun: The function used to calculate bar heights. Defaults to mean. Must return a single number.
errorFun: The function used to calculate error bar positions. Defaults to ciMean. Must return two numbers (lower and upper bounds). Set to FALSE to suppress error bars.
yLabel: The y-axis label. Defaults to the name of the response variable.
xLabels: Labels for the x-axis tick marks. Defaults to the levels of group1.
main: The plot title. Defaults to no title.
ylim: A numeric vector of length 2 giving the y-axis limits. The lower bound defaults to 0; the upper bound is estimated automatically.
barFillColour: A vector of colours used to fill the bars. Defaults to a pastel rainbow palette.
barLineWidth: The width of the bar border lines. Defaults to 2.
barLineColour: The colour of the bar border lines. Defaults to "black".
barSpaceSmall: The gap between bars within a cluster, as a proportion of bar width. Defaults to 0.2.
barSpaceBig: The gap separating clusters of bars, as a proportion of bar width. Defaults to 1.
legendLabels: Labels for the legend entries. Defaults to the levels of group2. Set to FALSE to suppress the legend. No legend is drawn when only one grouping variable is specified.
legendDownShift: How far below the top of the plot to place the legend, as a proportion of plot height. Defaults to 0.
legendLeftShift: How far from the right edge to place the legend, as a proportion of plot width. Defaults to 0.
errorBarLineWidth: The line width for the error bars. Defaults to 1.
errorBarLineColour: The colour of the error bars. Defaults to "grey40".
errorBarWhiskerWidth: The width of the error bar whiskers, as a proportion of bar width. Defaults to 0.2.

Value

Invisibly returns a data frame containing the factor levels, group summary values, and error bar bounds. This function is primarily used for its side effect of drawing the plot.

Details

Plots group means (or the output of heightFun) with error bars (or the output of errorFun) for one or two grouping factors. When two grouping factors are given, group1 determines the primary x-axis grouping and group2 determines the sub-grouping shown as clusters of bars with a legend.

Missing values are removed with a warning. At least 2 complete cases are required per group.

Examples

# one grouping factor
df <- data.frame(
  outcome = c(3, 4, 5, 2, 4, 6, 5, 7, 8),
  group = factor(c("a", "a", "a", "b", "b", "b", "c", "c", "c"))
)
bars(outcome ~ group, data = df)
#> Warning: longer object length is not a multiple of shorter object length
#> Warning: longer object length is not a multiple of shorter object length


# two grouping factors
df2 <- data.frame(
  outcome = c(3, 4, 5, 2, 4, 6, 5, 7, 8, 4, 3, 6),
  group1  = factor(rep(c("a", "b"), each = 6)),
  group2  = factor(rep(c("x", "y", "z"), times = 4))
)
bars(outcome ~ group1 + group2, data = df2)
#> Warning: data have zero variance