means_graph: Graph Means Across a Grouping Variable
In dvmisc: Convenience Functions, Moving Window Statistics, and Graphics

Creates plot showing mean of Y variable across levels of a grouping variable, with customizable error bars. Observations with missing values for y and/or group are dropped.

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means_graph(y, group, error.bars = "t.ci", alpha = 0.05,
  p.legend = TRUE, plot.list = NULL, lines.list = NULL,
  axis.list = NULL, legend.list = NULL, ...)

`y`	Numeric vector of values for the continuous variable.
`group`	Vector of values indicating what group each `y` observation belongs to. Function plots group levels across x-axis in same order as `table(group)`.
`error.bars`	Character string indicating what the error bars should represent. Possible values are `"sd"` for +/- one standard deviation, `"se"` for +/- one standard error, `"t.ci"` for 95% confidence interval based on t distribution, `"z.ci"` for 95% confidence interval based on Z distribution, and `"none"` for no error bars.
`alpha`	Numeric value indicating what alpha should be set to for confidence intervals. Only used if `error.bars` is `"t.ci"` or `"z.ci"`.
`p.legend`	If `TRUE`, p-value (from `t.test` function if group has 2 levels, otherwise `aov` function) is printed in a legend.
`plot.list`	Optional list of inputs to pass to `plot` function.
`lines.list`	Optional list of inputs to pass to `lines` function.
`axis.list`	Optional list of inputs to pass to `axis` function.
`legend.list`	Optional list of inputs to pass to `legend` function.
`...`	Additional arguments to pass to `t.test` or `aov`.