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Last data update: 2014.03.03

R: Plot with two y axes

y2plot

R Documentation

Plot with two y axes

Description

Function to plot two y variables, y1 and y2, against a single x variable, with the y1 and y2 axes on the left and right of the plot respectively.

Usage

y2plot(x, y1, y2 = NULL, labels, y2par = list(), add = FALSE,
  xy = NULL, xlegend = "topleft", inset = 0.04, ...)

Arguments

`x`	vector of ages.
`y1`	vector of measurements for plotting on left y axis.
`y2`	optional vector of measurements for plotting on right y axis.
`labels`	character vector containing labels for x, y1 and y2.
`y2par`	optional named list of par arguments to format the y2 axis.
`add`	logical flag to specify if a new plot (with axes etc) is to be drawn (FALSE) or an existing plot is to be added to (TRUE).
`xy`	optional list to pass `usr` and `usr2` (see Value).
`xlegend`	position for legend.
`inset`	inset for legend.
`...`	optional `par` arguments.

Details

y2plot draws up to two superimposed plots, one with the y axis on the left and the other on the right, with suitable adjustment for par('mar') and including a legend. The format for y1 is controlled by par arguments, and that for y2 by the list y2par.

Value

Returns the list

`usr`	par('usr') for y1 axis
`usr2`	par('usr') for y2 axis

In addition the variable .par.usr2, equal to usr2, is created in globalenv().

Author(s)

Tim Cole tim.cole@ucl.ac.uk

Examples

## plot boys median height and weight on the UK 1990 reference
with(uk90[uk90$sex == 1,],
  y2plot(x=years, y1=M.ht, y2=M.wt, y2par=list(col='red'))
)